The Mood Marker ～のだ

In our first lesson on ～のだ, we learned how its fundamental usage is as a “scope marker,” and in doing so, we learned a lot about how sentences with ～のだ are similar and dissimilar to typical declarative (肯定文) and negative (否定文) sentences, based largely on predicate type and the kinds of complements (補語) present in the sentence.

To begin our discussion on how ～のだ may set the mood of the sentence, we will uncharacteristically start with the conclusion. Mood, in grammar, may be described as any inflectional ending that describes the speaker’s attitude toward the situation at hand. As such, “mood” is highly subject to context. In understanding how the mood marker ～のだ functions, our discussion will demonstrate how the mood it sets is inherit to itself as well as borne from the context at large.

Before we get ahead of ourselves, let’s review once more what the terms “scope” and “mood” mean in the context of Japanese sentence structure and what the implications of those definitions have on the use of ～のだ.

Firstly, the nominalizing effect ～のだ has and its being part of the predicate are both intrinsic features. Secondly, Japanese sentence structure itself exhibits a strict hierarchy for what goes inside the predicate:

VERB STEM + VOICE + VOLITION + ASPECT + NEGATION + TENSE + MOOD

Meaning, ～のだ’s placement at the end both solidifies its position and functionality within a sentence. This can be demonstrated by the phrase:

食べられようとしていなかったらしいんだね .
Gloss: Eat-passive-volition-progressive-negation-past tense-mood (seems)-mood (reinforcement)-huh.
So it does seem (it) wasn’t trying to get eaten, huh.

Broken down, we have [食べ] as the verb root, [られ] a voice marker indicating the passive voice, [ようとし] indicating volition, [てい] indicating aspect, [なかっ] indicating negation, [た] indicating tense, and [らしい] indicates mood. It is arguably the case that [んだ]’s place in the predicate allows for it to function as a mood indicator.

Its nominalization effect on the conjugation chain is manifested by the copula portion in both its scope and mood marking renditions, but there are unique restrictions to the mood marker ～のだ not found with the scope marker ～のだ. That being said, keep the following points in mind when handling variations of the mood marker ～のだ.

Because the mood marker ～のだ reflects the attitude of the speaker, minute differences and restrictions can arise from whether it is contracted or in a different speech register; meaning, ～のだ・んだ vs ～のです・んです will be a matter of contingency this time.
As for whether だ is changed to dialectal variants such as じゃ・や, those will be treated as being synonymous.
Unlike the scope marker ～のだ, tense as well as affirmation vs. negation may interact differently depending on how the mood marker ～のだ functions. Meaning, whether those conjugations make sense is entirely dependent on whether those concepts are compatible on a nuance-by-nuance basis.

The Two ～のだ: “Scope” Marker VS “Mood” Marker

The main goal of this lesson will be determining the fundamental essence of the mood marker ～のだ, which considering how many specific nuances were mentioned, will be an arduous task.

The one commonality that links the mood marker ～のだ with the scope marker ～のだ is that they are etymologically the same, and both possess the same conjugations, but the functionality of the mood marker ～のだ goes beyond making predicates behave more like noun-predicates.

Providing an “association (関連付け)” is a great place to start when trying to understand how mood marker ～のだ works. The most typical examples one can find of it do, in fact, behave like this. First, consider the following.

1. セス君？いないよ。出張に行ったんだ。
Seth-kun? He’s not here. He went on a business trip.

The mood marker ～のだ in Ex. 1 serves to demonstrate to the listener that [出張に行った] is the situation behind [（セス君が）いない].

From Ex. 1 alone, it is evident that the mood marker ～のだ is a rather different beast than its scope marker counterpart. Instead of defining a Y¹, which is at the foundation of the scope marker ～のだ, the mood marker ～のだ seems to relate its comment to the context at large.

Incidentally, we also see a major difference in particle usage within the dependent clauses made by these two different ～のだ regarding は vs が. In the case of the scope marker ～のだ, は must never be used, but this restriction does not exist for the mood marker ～のだ. This does not mean that は does not occur with the former. Rather, は cannot exist within the confines of Y in the sentence pattern XはＹだ as this pertains to the scope marker ～のだ.

In the following examples, to make identification easier, X for the main clause, if present, will be put in 【】and が・は inside dependent clauses will be greyed. The extent of influence ～のだ has will be denoted by [].

2. テイラー君から【返事】来ないね。[きっときょうは忙しい]んだ。(Mood ～のだ)
I haven’t gotten a response from Taylor-kun. I’m sure he’s busy today.

3. [氷河期が来た]のではない。[地球温暖化が進んでいる]のだ。(Scope ～のだ)
It’s not that we have come upon an ice age. The issue is that global warming is progressing.

4. 【鉢の土は】、湿った状態だったので、[水が足りなかったから枯れた]のではありません。(Scope ～のだ)
The soil in the pot was moist, so it didn’t wither because of a lack of water.

Another grammatical difference between the scope marker ～のだ and the mood marker ～のだ is that the latter freely attaches itself to nominal/adjectival-noun predicates, whereas the former stipulates that the redefining be on X (think back to Ex. 21 in our coverage here). That is not to say that the scope marker ～のだ is incompatible with these predicate types, as Ex. 5 is an example of it, but there is no such hurdle as demonstrated by Ex. 6.

5. 何もしないのが休憩なのだ。(Scope ～のだ)
Doing nothing is what is defined as a break.

6. いま休憩なんだよ！(Mood ～のだ)
I’m on break right now!

7. メール確認は休憩なのでありません。仕事なのです。△ (Scope ～のだ)
Intended: Checking e-mails is not breaktime; it’s work. ?

Commonalities between both types of ～のだ can, though, be found in their shared use of the nominalizer の. One of which is that の makes the Y sound like an established entity, not reflective of a spontaneous matter.

8. どうしよう・・・うん、やっぱ行くんだ！X (Mood ～のだ)
Intended: What to do… Yeah, I will go!

The ungrammaticality of Ex. 8 is not due to やっぱ行くんだ itself being faulty, but that ～のだ (both types) is inappropriate for stating the speaker’s volition in real-time.

9. もう諒君には会うのではない。X (Scope ～のだ)
Intended: I’m not going to see Ryo-kun anymore.

This property is also what enables ～のだ (both types) to make third-person statements regarding thoughts and feelings, which is generally not done with predicate types in their basic iterations.

10. 諒君はきっと嬉しいんだ。(Mood ～のだ)
Ryo-kun is definitely pleased.

11. 思い出が悲しいのではない。思い出を美化するから、悲しいのだ。(Scope ～のだ)
It’s not that memories are saddening. It’s how (people) romanticize memories that is what is saddening.
Quote by 秋元康.

12. 私が悲しいのではない。悲しみが私に纏わりついて離れないのだ。(Scope ～のだ)
It’s not that I am sad; it’s that sadness clings to me and won’t let go.

2 Factors, 4 Combinations

Earlier, it was mentioned that the mood marker ～のだ inherently pertains itself to something the speaker views as an established situation, and with that in mind, consider the difference between the following.

13a. あ、雪が降ってる！
13b. あ、雪が降ってるんだ！
13a. Ah, it’s snowing!
13b. Ah, so it is snowing!

13a is a reflection of the speaker going outside and simply commenting on their discovery of it snowing. Meanwhile, 13b. recognizes the snowing as something that has been a thing, although they personally are just realizing it at the time of utterance. While “snowing” is perceptualized as an “established situation,” it is not the case that there was any previous context that would have definitively indicated “snowing” as being established fact. This is important to keep in mind, because it throws a wrench in the notion that mood ～のだ simply associates a statement with prior context for some explanatory purpose. As such, we can view statements like 13b. as cluing us in to more so the speaker’s state of mind than anything. In this case, 13b. matches with the “exclamatory sense of discovery = 発見” nuance listed in the earlier chart.

To account for all the nuances mood marker ～のだ has, two factors must be kept in mind. Insofar, these factors will be applied only to declarative sentences (平叙文).

Whether or not mood ～のだ relates its statement to previously stated context.
Whether mood ～のだ presents a matter to someone else (interpersonal) or is instead directing attention to the situation itself (interpropositional).

Interpersonal VS Interpropositional

One striking difference between interpersonal mood ～のだ and interpropositional mood ～のだ is that the latter does not pair well with polite speech registers, or with any tone adjustment, as the commentary is not meant to be directed at anyone.

14a. セス先生が来ないなあ。きっと用事があるの。??
14b. セス先生が来ないなあ。きっと用事があるんだ。◎
Seth-sensei hasn’t come, huh. He almost certainly has errands to do.

While the context may very well be an epiphany by the speaker on the matter at hand, and while the comment could be made within a back-and-forth discussion, lightbulb moments are more so for the speaker themselves mulling over the matter, and in doing so, the nuances （再）確認・発見 enumerated earlier are to be expected.

If interpropositional instances of mood ～のだ are self-directed commentaries, we would expect for it to pair perfectly with ～と思う and the like, encapsulating the speaker’s mood within the speaker’s own thought. Conversely, that dynamic would result in an ungrammatical statement (or an unintended interpretation) if applied to interpersonal instances of mood ～のだ.

15. セス先生が来ないなあ。きっと用事があるんだと思う。(Interpropositional)
Seth-sensei hasn’t come, huh. I think he almost certainly has errands to do.

16. 僕、明日は来ないよ。仕事があるんだと思う。(Interpersonal) Ｘ
I’m not coming tomorrow. I think it’s since I have work. X

17a. このスイッチを押すんだと思った。(Interpropositional)
I thought, yeah, I’d flip this switch.

17b. このスイッチを押すんだと思った。(Interpersonal) #
Intended: I thought, yeah, I’d flip this switch.
Result: I thought, “flip this switch!”

It goes without saying, though, that paying attention to context is of utmost importance. In isolation, non-interpersonal and interpersonal instances will often appear identical. Tonality alone may, though, be enough to delineate between non-interpersonal and interpersonal nuances most of the time. Even so, how the previous sentences or the situation in which the speaker finds themselves in matter at all would be left to speculation—speculation which Japanese discourse arguably necessitates. In other words, the “why” and “how” aspects of mood ～のだ are both being considered with what little or no context is being provided.

With all this being said, consider the following without context, and most importantly, without English translations, but with the likely nuances intended left in Japanese as hints.

18a. このスイッチを押すんだ。（確認・発見・強調・換言？）

18b. このスイッチを押すんだ！（決意・命令）

18c. このスイッチを押すんです。（決意）

18d. このスイッチを押すんです！（決意・命令）

Simplicity is only as simple as the context allows it to be, but that is where native-like intuition for deciphering even not-so contextualized contexts begins. In all four context-less scenarios, nuances are ruled out, which is a major takeaway.

Although 18a seems to have an array of interpretations, one can still surmise that the speaker is collecting their take on a matter with mood ～のだ, and the exact purpose (the “why”) would be made clear with preceding context or other outstanding factors, such as whether or not the speaker is alone, whether or not the speaker is talking (directly) to someone, or whether or not anything else had even been said. All these factors would be given facts pertaining to the discourse at hand and readably analyzed by the speaker and potential listeners.

Now let’s add minimal context. In doing so, we will see that not only does the nuancing of mood ～のだ become clear, if not outright obvious, but that that also necessitates that other nuances of mood ～のだ could highly unnatural, if not ungrammatical at worst as a result.

18e. そうか、このスイッチを押すんだ。
i. Oh, thus (X) flipping this switch. (再認識)
ii. Oh, you flip this switch. (発見)
iii. Oh, which is why you flip this switch. (確認)
iv. Oh, so flip this switch. (命令) X
v. Oh, you flip this switch (, so you know). (教示 ??・告白 ?? ・強調 ???)

Interpretations i-iii are all instances of non-interpersonal ～のだ, and while it may be vexing to be still left with multiple interpretations, external factors would otherwise assist. For instance, with i., knowing who the agent (=doer) is would tremendously help in knowing why the speaker is acknowledging flipping the switch has some importance in the overall scheme of things. As for ii., potential scenarios for how self-discovery on what happens when a certain switch is flipped comes into play are easy to imagine. Perhaps you are in a dungeon course, and you have been wondering how to get to the next room. You suddenly come across a panel and surmise that pressing the one with an ON/OFF switch will unlock some nearby passageway. iii. is more or less the same as i., but the epiphany is being attributed to outsider information. Someone else is present, but the actual statement is not being directed back at the listener to impose one’s own recognition of the matter to the entity that made it possible. Such a bizarre turning of the tables on what ought to be merely recognition of some greater importance on the part of oneself is precisely why v. is unnatural (but not entirely inconceivable). For instance, say そうか were not being used to acknowledge a previous statement but were more so indicative of a spur of the moment need to indicate that the statement marked by ～のだ is what the listener ought to hear – not to be confused with a lightbulb moment. In that scenario, what the speaker comes up with themselves could be pushed onto the listener as to what is the case or should happen, but the execution would still be unnatural, as all usages of ～のだ imply a certain level of conviction reflecting the speaker’s affirmation. Likewise, making an outright command (iv) in this manner remains ungrammatical, as commands made with mood ～のだ, while always interpersonal, do not occur out of the blue.

To visualize these two factors—interpersonal (対人的) and interpropositional (対事的)—of mood ～のだ, the following chart illustrates them with directionality at the forefront. Rather than viewing them as opposing meanings, they are juxtaposed in a way that highlights how they relate to each other.

In a way, interpersonal ～のだ is like superimposing a thought bubble regarding a matter onto the listener, with the presumption that the listener does not know along with the assertion that the situation ought to be known or potentially dealt with (by the speaker and/or listener).

Incidentally, this presentation on the part of interpersonal ～のだ is not the same as merely presenting a fact the speakers knows that the listener happens to not know. In such a situation as that, we find that not using ～のだ is, indeed, the natural route. Consider the following.

19. 晩御飯も寿司だった。
Dinner was also sushi.

20. 自販機も便利だった。
The vending machines were also convenient.

21. 「セス先生、今度の旅行先はどこですか」「もちろん、東京ですよ」
“Seth-sensei, where are you going on your next trip?” “Tokyo, of course.”

When it comes to simple (adjectival-)noun predicates, presenting a simple answer (=statement), we see that while mood ～のだ is not present, the idea of presenting a situation to the listener is still at work, which in that sense, these sentences greatly resemble interpersonal mood ～のだ.

Similarly, a parallel connection can be made between interpropositional mood ～のだ and (adjectival-)noun predicates, especially when rendered in their suppositional forms so as not to direct the statement back to the listener.

22. 「日本で地震が一番多いのはどこだろう」「うーん、恐らく福島県だろうな」
“Wonder where in Japan has the most earthquakes.” “Hmm, probably Fukushima Prefecture.”

23. 滋賀県の北西はどこだったかな。そうだ、琵琶湖だ！
The northwest of Shiga Prefecture, where was that? Oh yeah, Lake Biwa!

Even though there happens to be two speakers in Ex. 21, the response by the second speaker is directed toward the situation rather than the other speaker (=listener).

Now, in similar situations as is the case for the scope marker ～のだ, mood ～のだ also finds itself grammatically necessary, particularly with verbal predicates. While on the surface, the representation of verbs (=actions) may seem simple, on closer inspection, actions almost necessitate attention as to why and how the action is so, which is just the frame of mind for mood ～のだ to intervene. Next, consider the following.

24. 「昨日はどこに行ったんですか」「原宿に行ったんですよ」
“Where did you go yesterday?” “I went to Harajuku.”

25. 「テイラー君ったら、一体どこにいるんだろう」「うーん、きっと地元に行ったんだ」
Where on earth could Taylor be?” “Hmm, he must’ve gone back to his hometown.”

In Exs. 24-25, ～のだ is grammatically necessary. While ～のだ’s syntactic properties can be mostly attributed to the nominalization effect of の itself, the verbal dynamics at play, in tandem with the speaker’s mood toward the situation, make it quite different from basic noun-predicates seen in Exs. 19, 21-23. Moreover, mood ～のだ is fully capable of attaching itself to such (adjectival-)noun predicates, so that layer of meaning has to be accounted for.

By examining sentences like Exs. 21-23 in which mood ～のだ is not triggered, we see how when the speaker does emphasize the situation (事態) as being noteworthy, for whatever reason, be it to themselves (interpropositional) or to the listener(s) (interpersonal), ～のだ obligatorily appears.

In pursuit of how this extra layer of meaning comes about, there is one grammatical feature that has yet to be mentioned, and that is allowing the particle は in clauses made with mood ～のだ, irrespective of part of speech. This property makes ～のだ syntactically different than typical embedded clauses in nominalized expressions². Next, let’s look at another set of examples in which mood ～のだ’s presence does indicate more meaning than if it were omitted.

26a. 「Where are you from?」「アメリカから来ました」
26b. 「Where are you from?」「アメリカから来たんですよ」
Literally: “Where are you from?” “I came from America.”
“Where are you from?” “I’m from America.”

While either response is natural, 26b. is undoubtedly a more emotionally driven response than 26a, and the motive behind that kind of response is highlighting the fact presented to the listener for whatever reason. Perhaps the second speaker is someone who just got off the plane, decked out in American flags, and is bringing attention to the situation [アメリカから来た] for personal PR.

27a. そうだ、月曜は閉まってるんだ。
27b. そうだ、月曜は休みだ。
27c. そうだ、月曜は休みなんだ。
That’s right, they’re closed on Mondays.

27a and 27c are synonymous and are semantically and syntactically equal. In both versions, the speaker’s thoughts toward the situation at hand help indicate that the circumstances involved are why the establishment is closed on Mondays. Meanwhile, 27b is merely a reminder of the establishment being closed on Mondays, with no hint as to how come.

Relating Q to Previous Context: P = Q or P ≠ Q?

Another factor behind mood ～のだ is whether or not the situation at hand which has not been recognized (hereby referred to as Q)—with the people not recognizing Q as such dependent on the previous factor—is presented as the meaning/situation behind a previous context (=what has been said or established to be so, hereby referred to as “P”). When combined with interpersonal and interpropositional contexts, the resulting four outcomes are as follows:

The following four examples represent their respective combination.

28. テイラー君が来ないなあ。きっと何かがあったんだと思う。(Interpropositional, P=Q)
Taylor-kun hasn’t come, huh. Something must’ve happened.

29. 僕は明日は出勤しないよ。用事があるんだ。(Interpersonal, P=Q)
I’m not going to work tomorrow. I got errands to do.

30. そうか、ひっくり返して作るんだ。(Interpropositional, P≠Q)
Oh, you make it by turning it upside down.

31. 前へ進むんだ！(Interpersonal, P≠Q)
Keep moving forward!

Supposing that the basic sentence structure is presumed to remain as XはYだ even when the mood marker ～のだ is employed, in this light, [X=P] and [Y＋のだ = Q]. When X is not present, however, it would seem fair to posit that P≠Q in these cases; yet, there still seems to be some trigger for Q to be recognized even without a stated P.

To explain situations when P seems to not be present at all, P can be akin to the background situation=context at large. Even when that context appears to be missing, especially in the case of Ex. 31, the situation (Q) remains, meaning there must still be a trigger for Q’s realization. In which case, if P=Q is to hold true, then P need not be constrained to a prior verbal statement of the established situation but can be more broadly defined as situational stimuli/information that triggers the ascertaining of Q for that established situation. Even so, “P would not be Q (P≠Q)”, rather “P would prompt Q (P ⇒ Q).

To further delineate these two separate Ps from each other, P_v will hereby stand for verbalized/unambiguously indicated context that relates to the established situation (Q), whereas P_nv will hereby stand for latent, unverbalized stimuli/information at the time of utterance that prompts the speaker to recognize an established situation (Q). As such, [P_v ≈ Q], while [P_nv ⇒ Q].

The one situation that may seem too incongruent with this analysis would be commands made with mood ～のだ. Yet, the mood behind said commands does indicate a greater context (trigger) than if one were to use the imperative form (命令形).

31a. このボタンを押せ。
31b. このボタンを押すんだぞ。
Press this button!

While both translate as “press this button!” in English, Ex. 31b gives the impression that the speaker has analyzed the situation and has determined that this command is what the listener ought to do. Perhaps, even, talk had been had that the speaker is privy to, which further prompted this command³. In which case, the distinction between P_v and P_nv would be purely circumstantial. If so, we would imagine that there would be contexts in which delineating [P_v ≈ Q] and [P_nv ⇒ Q] would be difficult at face value, and lo behold, such contexts are quite common.

32a. 本、たくさん読んでるんだ（なあ）。
32b. 本、たくさん持ってるんだ（なあ）。
32c. 本棚が７つもあるんだ（なあ）。
32a. (He) sure reads a lot of books.
32b. (He) sure has a lot of books.
32c. Huh, (he) has seven bookshelves.

As for the context, imagine the speaker of Ex. 32 visiting Seth-sensei’s library. The room has seven bookshelves with many books, and these are 3 possible comments the speaker could make, all of which are interpropositional and examples of talking to oneself.

Books are meant to be read. Walking in and seeing bookshelves with lots of books, knowing that one is visiting Seth-sensei’s library and how he must read for his profession, conversations that may have been had prior, etc. all constitute as P_v, with P_nv as an extra bonus upon seeing the library for oneself—thus also explaining why the speaker readily understands Q. Meanwhile, Ex. 32c feels more like just a response toward the visual information (P_nv). Now, as for recognizing “Seth-sensei having a lot of books” as Q like in Ex. 32b, whether P_v is involved is up in the air. The speaker presumably knows they are about to go to a library, but perhaps nothing about the library has ever been ascertained until entering its doors. With either scenario being equally plausible, and with Ex. 32c being just as valid as a response as Ex. 32a or Ex. 32c, how the speaker ascertains P may very well affect what the speaker ultimately states as Q; however, if P=Q, and if situations (Qs) can be multi-faceted, then this really is just nitpicking at P(_n)⁴, with _n standing for tackling what Q is from all possible angles.

Relating [P_v ≈ Q] to XはYだ: [X=P_v] は[Y+～のだ=Q]

Now, let’s relate mood ～のだ back to “XはYだ” once more, but in the context of nominal predicates, given how nominal predicates state how the predicate equates to X. 寺村 (1984) points out that, principally, with mood ～のだ, P_vはYだ is no different than XはYだ. To demonstrate this, the following examples were raised:

40. あの音は何だ？
Response A: あれは鳩が鳴いている声です。
Response B: あれは鳩が鳴いているのです。

In Ex. 40, both responses identify what the noise (X) is. Response A goes down the grammatically most simplistic route by means of XはYだ: X is the noise and Y [鳩が鳴いている声] is the noise described. Meanwhile, Response B adds ～のだ into the fray, in which case, [X=P_v] and [鳩が鳴いているの] is still the “what” (Y) but as Q. Theoretically, both responses are synonymous as a consequence; yet, there still remains a palpable difference in nuance between them. This is because Q is no ordinary nominal Y: it is the situation at hand that is being tied back to the questioner’s concern.

41. [Context]: Detective sees bloodstains on a suspect’s shirt)
これ（＝この血）は何だ？
Response A: これは自分の鼻血ですよ。
Response B: 鼻血がついたんですよ。
Response C: 血です。???
Response D: 血がついたんですよ。??

In Ex. 41, the question XはY? is loaded by nature. Incidentally, it is this “loaded” nature of the question itself that affects how nominal Ys and nominalized Qs are mirror images of each other at best. The questioner wants to know whether the blood on the suspect’s shirt is related to the “case” at hand. Thus, there is unequivocally a P_v involved, and this is where the “loaded” nature of the question derives.

Response A is plain and simple: X is just the suspect’s own nosebleed (Y). In Response B, 鼻血がついたん (Q) is how P_v (the blood at hand being talked about) got on the suspect’s shirt, which can then also be internalized as “what” is going on. While this Q is still a “what,” [鼻血がついたん] it is not 100% like the nominal Y [自分の鼻血] found in Response A.

As for Response C, this is simply a non-answer, ignoring what the questioner is really asking, and it is just as frustrating to be responded in this way in English as it is in Japanese. Similarly, Response D is not only just a non-answer to the question but one that adds even more questions to the questioner’s mind as to “what” the responder is talking about. The P_v (blood on the shirt being talked about) is already established, so why present that in a way as if it is not unless there is another “what” which explains the stain? Even so, the framing would be faulty=ungrammatical for not presenting the right Q.

To summarize, the limiting of Y to nouns in the fullest sense in the structure XはYだ keeps this basic sentence pattern grammatically restricted, and that P_vは[Yのだ=Q] helps extend this basic grammar but at a cost. This “cost” is the declaration of Q as pertaining to P_v, which is a more complicated relationship than those made by simply stating that X=Y, explaining how our parallel examples above are so similar yet different. As far as how ～のだ ought to be defined, perhaps the answer is as simple as P_v (context) being defined as Q within the confines of its own flexibility, that being the myriad of ways that can be interpreted with context heavily influencing what both P_v and Q are.

In other words, as much as we might want X to stand for anything, nouns alone cannot suffice to represent anything. The context at large, however, can stand for anything. When we wish to define that context, the inability of X to fulfill that role triggers the transformation of XはYだ to P_vはQ. Thus, [X=P_v], but most importantly, [P_v≈Q], with the swapping of ≈ for = indicative of the structure’s inherent flexibility in utility and interpretation.

Something we shall see in great detail in our third lesson on ～のだ, this triggering can even be combined together via dependent clauses as such:

42. [[ここまではわりにきっちりと書いてある = P_v^A]。[ところが早くも飽きてきたのか = Q^{1 of PvA}]、[それとも書くことがなくなったのか = Q^{2 of PvA}]、ここで三日ほどブランクがある = P_v^B]。[いきなり五月五月十二日になっているのだ = Q^{1 of PvB}]。
From 『むかし僕が死んだ家』by 東野圭吾.

Also note that, Y, in the context of XはYだ is also limited to nouns, so if an association is really being made between two thoughts, it ought not have that restriction placed on it. This may make you think, “well, what about nominalization? Is that not what ～のだ does to a Y which is not a noun?” That is precisely what happens, but it is crucial to note that nominalization is a transformative process. To see this in action, look no further than ～のだ predicates involving origin. Here, we see that XはYだ in its basic form of X and Y both being nouns is often impossible.

43. これは彼氏にもらったんだ。
This, I got it from my boyfriend.

44. これは彼氏の好きなものの中から選んだんだ。
This, I picked it out from the things my boyfriend likes.

While XはYだ cannot be extended as is to accommodate more complex scenarios, P_vはQのだ by extension allows it to.

Incidentally, there are sentences in which X is a nominal phrase created through nominalization via の, but this is not problematic in determining how mood ～のだ functions. In this case X[～の] still gets transformed into a P that is then associated with a Q via ～のだ. Such sentences also indicate how scope ～のだ and mood ～のだ are ultimately, also, one and the same.

45. 制度に驚くのは、ものの考え方に驚いているのだ。
Their surprise in (that) system is that they are surprised at their way of thinking. (Scope ～のだ)
They’re surprised at their way of thinking, as far as their surprise in (that) system goes. (Mood ～のだ)

Relating [P_nv ⇒ Q] to XはYだ: ([X=P_nv]は)[Y+～のだ=Q]

Earlier, we probed whether instances of mood ～のだ which seemingly do not pertain to previous context truly are without some sort of context. In reality, the context is visual stimuli in the moment, and in this sense, we yet again see similarities with certain noun-predicates. Consider the following:

46a. あっ、雨だ。
46b. あっ、雨が降ってるんだ。

47a. このボタンを押すんだ！
47b. このボタンだ！

In both situations, Q≈Pnv as opposed to Q≈Pv, as the Q at hand is not explicitly bound to any particular “previous context” as far as we can tell from just these wordings. Nevertheless, the interpretation of Q in both sentences tell us that a P exists in some capacity. There could be a myriad of ways in which the speaker of Ex. 46b realizes that it is raining, but while we may not know explicitly which stimuli got them to that realization, whatever it was prompted this sense of discovery. Likewise, there is something awfully important about pressing [このボタン], so much so that the speaker feels impelled to command the listener to get to pushing it.

When Q≈Pnv, the basic sentence structure XはYだ is not too dissimilar with P_nvは[Y+～のだ=Q]; thus, [X=P_nv]は[Y+～のだ=Q]. However, by nature of Pnv being latent information which would only be tangible in the deep structure of the grammar point itself, the surface structure that we see in action would necessarily be rendered as ~~([X=P_nv]は)~~[Y+～のだ=Q].

（以前にも通り越したことのある、ずらりと並んだ門を前に）
48a. 思い出した、一番右の門だ！　　　　　（確認）
48b. 思い出した、一番右の門を選ぶのだ！　（確認）

（隊長が旗を振りつつこう叫ぶ）
49a. よーし、スタートだ！　　　　　　（命令）
49b. よーし、スタートするんだ！　　　（命令）

While hopefully an obvious facet of Japanese grammar by this point, it goes without saying that XはYだ can easily manifest as Yだ at the surface level. However, for a language which allows the ellipsis of any complement of a predicate deemed obvious enough, obligatory ellipsis can obfuscate the existence of said X elements altogether⁸. Nonetheless, these latent Xs, and by proxy, latent P_nv, help frame the narratives behind the use of an exclamatory tone, set by simple declaratives in Ex. 48a and Ex. 48b. and by the modal nuances of confirmation and command in Ex. 48b and Ex. 49b.

A Closer Look at the Four Combinations

Now that we have covered the basics, we will now take a closer look at the four distinct environments which define the mood marker ～のだ:

The interpropositional ～のだ wherein [P_v ≈ Q].
The interpropositional ～のだ wherein [P_nv ⇒ Q].
The interpersonal ～のだ wherein [P_v ≈ Q].
The interpersonal ～のだ wherein [P_nv ⇒ Q].

The Interpropositional ～のだ

Whenever the interpropositional ～のだ is invoked, the speaker presents Q as a situation deemed necessary to mention as they themselves have not recognized it as such up until the point of utterance. This presentation, however, is to themselves through their own monologue. For the moment, we will put aside the difference between P_v and P_nv to see what exactly interpropositional ～のだ provides to a sentence. First, let’s return to the following examples:

28a. テイラー君が来ないなあ。きっと何かがあったんだと思う。(Interpropositional, P≈Q)
Taylor-kun hasn’t come, huh. I think something must’ve happened to him.

30a. そうか、ひっくり返して作るんだ。(Interpropositional, P≠Q)
Oh, you make it by turning it upside down.

From these examples, we see that regardless of the nature of P, the use of ～のだ indicates that the speaker has had time to discern Q. Whatever the (latent) circumstance there may be, these sentences would be highly unnatural without ～のだ establishing that realization for what it is.

28b. テイラー君が来ないなあ。きっと何かがあったと思う。X

30b. そうか、ひっくり返して作る。X

Conversely, when the speaker does not have time to discern Q, a simple declarative predicate will likely suffice. Even if a relationship can be made between whatever P and Q, if Q cannot be discerned as being a situation worth coming to some realization for whatever reason, that greatly context is either irrelevant or nonexistent.

50a. あっ、ネズミが死んでる！〇
50b. あっ、ネズミが死んでるんだ！＃
Intended Meaning: Ah, (this/these) mouse/mice [is/are] dead!

Imagine walking out to find a mouse, or perhaps more than one mouse, dead. Terrifying. In the moment, Ex. 50a. is what you inevitably shout. There is no time for you to speculate any deep meaning into their deaths; you have simply stumbled upon their lifeless remains. And, that is the extent of your declarative sentence as an effect.

What if, however, you are in a lab that experiments on mice. You have monitored the mice for some time, but then you notice, uh-oh, the mice are no longer moving. Mind you, you had tweaked the compound you were injecting them on the daily oh-so slightly only a few hours prior. You poke them only to get no response; they are no longer among the living. In this scenario, Ex. 50b becomes valid, as there is a meaningful Q ascertained by the speaker.

Even for in-the-moment representations of events that are established in real-time before the speaker, we find that this lack of time to ascertain a Q blocks its manifestation, and thus, no ～のだ.

（ぎりぎりで終電に乗り遅れて）
51a. しまった、間に合わんかった！〇
51b. しまった、間に合わんかったんだ！＃

This does not mean that the phrase 間に合わなかったんだ is, itself, ungrammatical. The ungrammatically is due to no Q being substantiated. To understand this, compare with Ex. 52.

52. ああ、それでも間に合わなかったんだな。

Here, “not making it in time” is established, and the speaker has had time to assess how things transpired but also to come to the conclusion that [間に合わなかった] is the Q at hand.

What if, however, the speaker needs no time to ascertain Q? What if the speaker can immediately ascertain that a Q is and has been going on even as they are just seeing it now for the first time? It turns out such inferences are possible, and we need look no further than going outside and seeing children playing in the snow.

13a. あ、雪が降ってる！
13b. あ、雪が降ってるんだ！
13a. Ah, it’s snowing!
13b. Ah, so it is snowing!

As mentioned earlier, Ex. 13a is merely commentary on the fact that it is snowing, and the less heads-up the better to capitalize on that exclamation. Nonetheless, it is also just as reasonable to assume that the speaker realizes more significance to this discovery than just the discovery itself. If they are seeing children playing in the snow, then enough time has elapsed for there to be enough snow to make snowballs and throw them at each other. Seeing that then becomes the basis for Q.

Earlier, we also saw how ～のだ can be phrased out by reverting to a simpler XはYだ structure, with Y necessarily being a pure noun. In such rewrites, the appearance or lack thereof of ～のだ does little to the sentence other than a layer of nuance on the lines of “that must be it.” For instance, in Ex. 27c which is restated below, perhaps the statement was uttered after having tried opening the door to the establishment only to find it locked, whereas Ex. 27b might have been uttered upon having just remembered that they are closed that day.

27a. そうだ、月曜は閉まってるんだ。
27b. そうだ、月曜は休みだ。
27c. そうだ、月曜は休みなんだ。
That’s right, they’re closed on Mondays.

The idea of trying to open the door and finding it to be locked serves as information which gives a basis for the predicate constituting a Q, thus, ～のだ. Likewise, if the speaker is ascertaining a Q based on information obtained from say, the other person in the conversation, then we would expect the absence of ～のだ to be unnatural, or at the very least, not reflective of the interpropositional iteration of ～のだ.

Context: Noticing a jaguar in the distance, you ask your friend whether people get attacked by jaguars in the area, only to be told jaguars are not even there in the first place. Then, you spout to yourself, “hm, well, that can’t possibly be true (because you saw one just then).”

53.
「アリゾナ州には、ジャガーなんていないよ」「ちっ、嘘｛なんだ〇・だよ＃｝、それ」

Here, responding with 嘘だ would not be ungrammatical, but it would certainly be a direct refutation of the other person’s comment to their face. Meanwhile, with 嘘なんだ, the speaker is realizing to themselves that their friend is feeding them a crock of lies.

54a. 「ここには誰も住んでませんよ」「ふーん、空き部屋なんだ」
54b. 「ここには誰も住んでませんよ」「ふーん、空き部屋だ」＃
Intended Meaning: “No one lives here.” “Hmm, so it’s an empty unit.”

Of course, if the speaker of the second sentence has completely tuned out the other speaker and walks into a unit and sees that it is vacant, the use of Ex. 54b. becomes valid.

Now, one thing that plagues the mood marker ～のだ overall, both as is and when it is contracted in casual speech as ～んだ, is whether it is actually truly natural for it to manifest as is without the affixation of a final particle such as よ, な, ね. In the case of the interpropositional ～のだ, the final particleよ would not be compatible, but as we have seen in quite a few examples, ね⁹, な（あ）, or even よね・よな（あ）are quite viable. Even so, bare instances of the interpropositional ～のだ・んだ are possible, especially in the speech of younger generations, with だ-final sentences, in general, being more indicative of male speech.

52. ああ、それでも間に合わなかったんだな。

55. うん、確かに、歌詞って書けそうで書けないもんなんだね。

Another solution to potential unnaturalness from a bare instance of interpropositional ～のだ is the use of the final particle か as a rhetorical remark directed at oneself. However, one would still have to assess whether ～か or ～のか is appropriate based on whether there is a Q to be had or not.

54a. 「ここには誰も住んでませんよ」「ふーん、空き部屋なんだ」
54c. 「ここには誰も住んでませんよ」「ふーん、空き部屋なのか」

56a. 「あられが降ってきたぞ！」「ふうん、あられが降ってきたか」
56b.「あられが降ってきたぞ！」「ふうん、あられが降ってきたんだ」
56c. 「あられが降ってきたぞ！」「ふうん、あられが降ってきたのか」
56a. “It’s begun to hail!” Hm, it’s begun to hail, you say.”

The simple use of ～か indicates the speaker’s withholding of making an assessment in the affirmative that they necessarily believe what the other person has said. Meanwhile, Ex. 56b. has it that the second person now recognizes the situation for what it is. However, some speakers might find it rather odd to be restating what someone has just told you as new information in a declarative in this manner. To alleviate this, though, Ex. 56c does not have that problem. It enables that speaker to recognize Q but also hold off on believing Q for what the first speaker says until they get to see the hail falling from the sky themselves.

Context: Seth-sensei looks at his computer’s time as he writes this lesson and sees that it is already 10 PM:

57a. あ、もう２０時か。
57b. あ、もう２０時なのか。

In the case of Ex. 57a, as one can expect, this is merely a statement of Seth-sensei realizing what time it is. If, however, 10 PM were his bedtime but he really wanted to finish writing the lesson, we could expect Ex. 57b instead.

The Interpropositional ～のだ wherein [P_v ≈ Q]

Having ironed out more details about the interpropositional ～のだ in general, let’s next narrow our focus to when it is being used and it is already a given that Q≈P_v.

As for the sorts of relationships Q and P_v may establishing together, while quite varied, the situation interpropositional ～のだ may be simply explained as the speaker’s attempt at processing the situation at hand/pre-existing context in a way that is easi(er) to ascertain (Q). It could be the case that Q is the situation as perceived from P, or Q might very well be a rephrasing/defining of P (換言).

Context: You see your friend driving. You did not know she owned a car, let alone could drive.

58. あ、由起子さん、運転するんだ！

It is not just that she is driving, but that she drives as in on the daily. This assertion (Q) is made possible by inference from what is being observed.

59.「一週間に、レッスンをいくつぐらい作れるんですか」「いつく作れるんだろうな、月に平均３つくらいは作っているように思いますが」「とすると、年間４０個未満作り出せるんだ！」

Here, the Q [年間４０個未満作り出せる] is quite literally a rephrasing of its P [月に平均３つくらいは作っている].

The Interpropositional ～のだ wherein [P_nv ⇒ Q]

If the interpropositional ～のだ is invoked and it is the case that [P_nv ⇒ Q], the speaker is grasping at the moment of utterance what Q is thanks to P_nv.

So far, we understand P_nv to be the overarching context which prompts the ascertaining of Q, with said context latent in nature in that neither the speaker nor other parties are actively causing the realization to happen.

60. そのとき、ドアが開いて、入ってくる遼平。一同、ハッピー・バースデイと歓声。さらに続いてくるセス。
セス「え、こんなに一杯いるんだね！」

It is Ryohei’s birthday and he and his partner Seth have been invited over to a friend’s house to celebrate. Both are aware that there are going to be others present, but to what extent, there is a presumption that, ideally, it would be enough to make the celebration feel worthwhile. Then, the moment of truth – Ryohei opens the door and all their friends and family are there with a good old “Happy Birthday!” His partner’s response reflects a realization of just how many people showed up upon seeing the crowd himself.

While it may seem tempting to relate the large crowd’s presence and the verbalization of that large crowd’s presence as one and the same. In other words, if Seth sees how many people there are, and it is a given that they have been there, then would Q not be equal to P_nv? The issue with this is that it is not just that a large number of people are there. In fact, Seth could have simply responded with:

61. え、こんなに一杯いる・・・

If this were Seth’s reaction, then the statement would only describe the crowd and nothing more: “whoa, there is a lot of people.” Yet, by using the interpropositional ～のだ, the true realization behind Q is that the presence of all those people ties back to just how many people really do care about Ryohei enough to be there in solidarity. That love and care counts as an established situation (既定の事態) being recognized for what it is at the time of utterance.

Sometimes, a realization of Q is not always the first time that realization has been made, but as far as that realization is concerned at the time of utterance, that would be a re-recognition on the part of the speaker. Of course, some P_nv will be responsible for triggering the speaker’s memory.

48c. 思い出した、一番右の門を選ぶんだよな！

62. （日本酒を飲んで）
うまいんだよな、これが。

Up to this point, we have defined P_nv as follows:

Latent, unverbalized stimuli/information at the time of utterance that prompts the speaker to recognize an established situation (Q).

While this definition does account for all instances of P_nv shown thus far, there is another source of P_nv that throws a wrench into this definition: when P_nv is a comment made by another entity (heard or read) by the speaker that prompts their spontaneous realization of Q. This realization of Q is phrased by repeating the quote verbatim or a near-identical paraphrasing, and while a third party is necessarily responsible for the remark, the information generated is treated as external stimulus which triggers the realization of Q.

63.「大谷選手がパパになったって！」「へえ、パパになったんだ」

Q is, as we have come to learn, is never just as simple as stating a reality in plain terms (Ex. 60 vs Ex. 61) or something that is 100% how something would be envisioned. Meaning, there is something significant about coming to the realization at hand in and of itself.

64a. 思ったとおり、友達がいっぱいいる。〇
64b. 思ったとおり、友達がいっぱいいるんだ。X

Before we slightly redefine P_nv to account for this environment, it is important to remember that all environments of mood marker ～のだ pertain to established situations. Not only that, the sentence or sentences involved—depending on which environment—are all stated once the speaker has had time to ascertain Q. Even when it seems that the realization is spontaneous, the speaker must have prior context (P_v) or some trigger (P_nv) for the lightbulb moment to occur.

Meaning, while the presenting or grasping of Q might be done at the time of utterance, if not enough time is provided for the speaker to come to the understanding that Q is there, then Q does not exist. To account for this, when Q is ascertained via a listener or other form of media, this third-party auditory/written stimulus is treated as a trigger, yes, but the Q will still necessarily be something that the speaker could have come to the realization beforehand.

To visualize this, imagine you turn on the TV and the first thing you see is footage of the capital of your country under attack by aliens. A perfectly reasonable reaction to this footage could be…

65. う、宇宙人が攻めてきた！？これ、嘘だろう？！

…in which ～のだ is not employed. Posit, however, that, instead, you have heard rumors of the capital being attacked by aliens. You find it hard to believe. Yet, you eagerly await the evening news report to see if anything is mentioned about the attack. If anything, you are hoping that it was just an AI-generated clip. As you eagerly await the evening news, you start hearing large explosions out in the distance. You rush to your TV and turn it on, only to see the following caption:

66. 宇宙人が襲い掛かる、死傷者が１００万人超と推定

In this light, we might expect our now terrified citizen to respond with:

67. やばっ、宇宙人が襲い掛かってるんだ！

Out of sheer disbelief, we would also be more likely to hear ～のか used somehow instead to make for an even more natural response. In either event, the role of interpropositional ～のだ with spelled-out P_nv as the trigger is made clear. Q is more so that the alien invasion is very much real and a really, really big deal. If ～のだ were dropped, the comment would still be grammatical, granted that the speaker is not coming to any sort of realization, but it would lack reference to that greater realization. It is also worth noting that neither the AI-generated clip nor the explosions nearby would constitute Pv. Additionally, we would imagine that if Q is being realized as P_nv verbatim that we could theoretically paraphrase any example to fit [P_v ≈ Q], at the cost of changing the mood, of course, to follow a chain of logic as opposed to blurting out a realization. Consequentially, this paraphrasing process also necessitates that Q be more collected given the additional time at hand, which is also used to put together an association between Q and P which would have otherwise not taken place.

68. （遠く離れた首都圏の方向から爆発音が絶え間なく轟いているのに気づき、心配でニュースを確認すると・・・）
う、宇宙人が東京を攻撃しているんだ！

69. 宇宙人は今、東京や北京、ワシントンDCなど、各国の首都を集中的に攻撃している。つまり、地球全体の政府機関を完全制圧しようとしているのだ。

As for simple examples like Ex. 63, it may appear as though [P_nv = Q].

63.「大谷選手がパパになったって！」「へえ、パパになったんだ」

As a mood marker, though, even the feeling of surprise ～のだ¹⁰ gives off provides it enough significance to distinguish it from simple regurgitation of a now-known fact. The significance (Q) is drawn there in the speaker’s mind. This is what mood marker ～のだ provides at a bare minimum. Ergo, when P_v is made available, that significance becomes more complex and integral to the statement at hand.

With everything that we have now learned, let’s define P_v, P_nv, as well as Q once more:

P_v: Unambiguously indicated context—either directly stated by the speaker or the speaker’s own two cents on the context at hand—that relates to the established situation (Q). Furthermore, the speaker must have had enough time to ascertain the connection being made between P_v and Q by them by the time of utterance.
P_nv: Latent stimulus or stimuli that come to the forefront—not discriminating sensory cues from those made through speech or the written word—at the time of utterance, prompting the speaker to recognize an established situation (Q). While the trigger(s) do not constitute Q itself, their foreseeability facilitates the recognition of Q by the speaker.
Q: The established (pre-existing) situation which presumably has not been recognized as such, either by the speaker (interpropositional) or by the listener (interpersonal) but is being grasped or presented as such at the time of utterance by being verbalized and associated with unambiguously indicated context from which it is based (P_v) or by being verbalized upon being prompted by latent stimulus or stimuli as triggers (P_nv).

The Interpropositional ～のだ in ～のだった

Incidentally, ～のだ possesses the form ～のだった for both its interpropositional and its interpersonal iterations. Given how the mood marker ～のだ itself is quite complicated as per the exact emotional effect it provides—highly context-dependent as we continue to discover—it would stand to reason that simply labeling ～のだった as referring to a certain mindset in the past would be insufficient.

As for the interpropositional ～のだった, there are two distinct yet closely related nuances that it may provide: “calling to mind precisely a Q that the speaker had forgotten sometime in the past” (想起) and “regretting that Q had not been realized at the time being brought back into the forefront” (後悔).

70. あ、今日で、もう終わりにするんだったな！(想起）

71. ああ、２年も延期されるのなら、自分で作っとくんだったわ！（後悔）

The first nuance of recalling Q to mind (想起) is not quite the same thing, however, as the interpropositional ～のだ’s nuance of re-recognition (再認識), which can be attributed to ～た’s own mood being added into the mix.

62a. （日本酒を飲んで）
うまいんだよな、これが。〇

62b.（日本酒を飲んで）
うまいんだったよな、これが。???

The trigger “sipping sake once more” prompts the speaker to re-recognize how awesome it tastes, but the deliciousness of the sake is not being reconfirmed in the sense that the speaker has forgotten about its deliciousness up until now.

72a. あ、第二月曜日は休みなんだ。
72b. あ、第二月曜日は休みなんだった。

As we learned earlier, we expect some form of Pnv to trigger the realization of Q in the case of Ex 72a., but as for what prompts the speaker to use ～のだった in Ex. 72b instead is to place emphasis on how something the speaker is not just re-recognizing the periodic closure but that it is something they had forgotten and are now reconfirming while also coming to terms with the significance that that fact holds, as prior to remembering, they would have continued being under the presumption that the establishment was open.

72c. あ、第二月曜日は休みだった。

The significance of Q, in many simple situations where it may seem hard to read into the statement, may, in fact, be negligible to the point that its absence does not change the statement all too much. Of course, the statement becomes a simple declarative, and there is no Q to be read in the statement. However, it turns out that the mood of ～た can suffice to indicate “recollection.”

As for ～のだった’s ability to indicate regret, this is made possible when there is a perceived consequence for not having recognized Q sooner. Meaning, by default, this nuance is only found with verbal predicates, specifically only those pertaining to volition of the agent=speaker (意志動詞). Ultimately, this nuance is a highly restricted sub-nuance of the first. More importantly, as far as tense is concerned, whereas ～のだった’s “recalling Q to mind” does involve forgetting about Q sometime in the past, the event/action involved is not restricted to the past, but with its nuance of “regret” of not realizing Q sooner, the action solely pertains to the past and in a counter-factual way to emphasize the lack of foresight on the part of the speaker=agent.

73.しまった、こんなことなら、最初に携帯の番号くらい聞いとくんだったな。

74. 「今度」はもうないんだった。

In Ex. 74, we know that there not being a “next time” is a future event, but ～のだった is used because this is a Q that the speaker should have already known but forgot but is now hitting home. While this is not the same as stating “regret,” this can be viewed as a bridging context for how that functionality came about.

The Interpropositional ～のだ in ～んだっけ

The realization of Q by the speaker may not always be the first time that realization has been made. When it is a re-recognition (再認識), the speaker still may not be totally sure that they got the right Q in their mind. When this is the case, we find that the final particle ～っけ may attach to the interpropositional ～のだ. In doing so, it usually appears contracted to produce ～んだっけ.

75. イースターっていつから商業化されたんだっけ？

You may also see ～んだったっけ provided that there is a presumption of having forgotten about Q while still not being sure one is entirely on the right track.

76. そういえば、大気汚染に配慮して、お線香の使用が禁止されたんだったっけ。

The Interpersonal ～のだ

Whenever the interpersonal ～のだ is invoked, there is always another person that the speaker is talking to, as Q is being presented to them. With the interpersonal ～のだ, it is already presumed that the speaker is fully aware of the Q that they are presenting to the listener before the time of utterance. For the moment, we will put aside the difference between P_v and P_nv to see what exactly the interpersonal ～のだ provides to a sentence. First, let’s return to the following examples:

77. テイラー君はいないよ。何かがあったんだ。

How the speaker ascertains Q and relates it to Pv in Ex. 77 may seem no different than how the interpropositional ～のだ functions. While this is, indeed, what they share in common, the speaker’s mood is notably different. In Ex. 77, the speaker is positive that something has happened to Taylor-kun, and not only that, they feel compelled to tell the listener about it. This desire to want the other party to be on the same page regarding Q is at the heart of how to use the interpropositional ～のだ.

As for the exact reason why the speaker is presenting Q to the listener, the reasons are quite varied. In the chart which prefaced this lesson, three nuances were presented, and in light of what we have lined, they can be redefined as such:

告白: Declaring Q, believed to be known only to the speaker up until the time of utterance, to the listener, which may be perceived as a confession.
教示: Explicating Q under the presumption that the listener is unaware, which may be done simply to teach the listener on the matter or to instruct them on it in some way.
強調: When the speaker feels as though the listener is not accepting Q the way they do, Q is underscored out of a plea for them to do so.

78. 僕って、遼平君の夫なんですよ。（告白）

79. 外国の方々もきっと同じように言語の壁に悩んでいるんですよ？（教示）

80. なにかあるの。絶対に何かあるんだよ。（強調）

While these three nuances reflect various nuances that come about from the speaker going out of their way to present Q to the listener under the presumption that the listener is not of the same understanding, the interpersonal ～のだ is not limited to them. Rather, these nuances come about from the dynamics happening within the discourse.

The Interpersonal ～のだ wherein [P_v ≈ Q]

With the exact reason why the speaker is going out of their way to make the listener perceive Q as they do may be varied, the significance behind [P_v ≈ Q] is never going to be simple as “that is that.”

First, let’s return to Ex. 77, which is a very typical instance of Q being presented as the circumstance behind P_v.

77. テイラー君はいないよ。何かがあったんだ。

Earlier in this lesson, we talked about how using the word “explanation” is a dangerous slope to oversimplifying the dynamics behind ～のだ, especially given how it is unequivocally NOT the same thing as saying “because.” In Ex. 77, it is not the case that the speaker is simply stating that “something happened to Taylor-kun” but that mentioning it provides context behind his not being there. In short, the speaker is, in fact, giving the listener a background explanation in a way that they might be content with how Taylor-kun is unaccounted for.

33a. 私は傘を見てぎょっとした。一面にびっしょり黴が生えていたのだ。〇
33b. 私は傘を見てぎょっとした。一面にびっしょり黴が生えていたからだ。〇
33a. I was startled when I looked at the umbrella: it was completely covered in mold.
33b. I was startled when I looked at the umbrella; this was because it was completely covered in mold.
From 『哀しい予感』by 吉本ばなな.

While parallels can be made between providing a background explanation and a reason for why an observation is being made, they are simply similar at best.

Also, because the speaker has already ascertained Q before the time of utterance with the interpersonal ～のだ, it can often be stated first with Pv stated after.

81a. 遼平が外で待ってるんだ、急がなきゃ。

Compare this to:

81b. 遼平が外で待っているから、急がなきゃ。

In Ex. 81a, the speaker’s choice to mention Q first with ～のだ provides an emotional appeal to the listener that they are more than aware that they need to hurry the heck up before even stating the P_v, which is presumed to be everything that they are hurrying which is preventing them from being outside with Ryohei.

Meanwhile, Ex. 81b, only states that they must hurry because Ryohei is waiting outside, with the emotional appeal to hurry up not nearly as strong as is the case with Ex. 81a.

The Interpersonal ～のだ wherein [P_nv ⇒ Q]

【参照】
「の（だ）」の機能 by 野田春美.

Even so, XはYだ can still be viewed as the basic sentence pattern for both the scope marker and the mood marker ～のだ. ↩︎
Think back to how the particle は cannot enter the scope of ～のだ when used as a scope marker. In this light, the way in which the mood set by ～のだ extends over the whole statement, as opposed to being locally limited to some scope, is not limited to noun-predicate-like grammar. Moreover, embedded clauses which modify nouns do not allow topicalized items to be inside them, defaulting to only marking the nominative case with が・の. ↩︎
Even if, for the sake of argument, that no such association with prior context or analysis of the greater situation at hand (P_nv)—the basis for labeling this as non-association (非関連付け) with P—were intentional on the part of the speaker, the implication of the command itself begs to differ, as there is an implied consequence to not following through, or that that is the course of action that needs to be made. Such inferences are only made possible by the existence of circumstantial input that is prompting the speaker to use the mood marker ～のだ to present Q in an imperative tone. ↩︎
Presenting grammar from a mathematical standpoint is incredibly helpful when understanding ～のだ as a whole. Complements are given letter substitutes, and differences in sentence structures (=equations) have to be accounted for so that the equations themselves do not break or contradict each other. Here, the issue really is what is Q, and by understanding Q, mood ～のだ’s meaning is ascertained. ↩︎
The use of 非関連付け would emphasize that because there is no verbalized/unambiguously indicated prior context, such context does not exist or is not being implicated; therefore, there is no explicitly stated association with P and Q (P≠Q). In this analysis, however, non-verbalized prior contexts—in whatever form of stimuli/sources of information they may take—are treated as playing an equivalent role to verbalized/unambiguously indicated contexts, and it is this differentiation among other factors which help properly ascertain Q. ↩︎
Confusingly, Ex. 34b would be presenting her suddenly looking up with that stern look as a situation in and of itself to bring attention to the reader, but we know that not to be the case, as this is her reaction to another Q (presumably their discourse with each other) and the reason for why the speaker stopped talking. ↩︎
Ex. 36a is even more confusing than Ex. 34b. In Ex. 36a, the speaker being injured is still being associated with falling down the stairs, but the association is not “falling down the stairs causing the injury”; instead, it is unclear how or when the speaker got hurt as well as how falling down the stairs fits in with that assertion. People can still be unscathed from falling down stairs, and a previous injury could have been a factor in falling down the stairs. ↩︎
Compare this to English where X always manifests out of grammatical necessity with just as “meaningless” subjects like the “it” in “it’s raining!” ↩︎
The use of ね alone does not convert ～のだ to its interpersonal iteration. So long as the statement is an affirmation of the speaker’s own confirmation of Q, ね would simply relay that self-realization to the nearby listener. ↩︎
This level of surprise cannot be understated, as even when P_v is at play, a certain level of disbelief at coming to the realization of Q sets the tonality of the statement marked by ～のだ and its variants. ↩︎

The Mood Marker ～のだ