Might: かもしれない
To describe a 50/50 probability that “may/might” happen, ～かもしれない is used. It is composed of the particles か and も followed by the negative form of the verb 知れる, which is an intransitive verb meaning “to be known/understood.”
Orthography Note: The Kanji spelling ～かも知れない is fairly common, although the Hiragana-only spelling is most prevalent.
ConjUGATING WITH かもしれない
The particle か follows the 連体形 of predicates, but with nominal (including adjectival nouns) predicates, the copula must be deleted. It may also follow both the non-past tense and the past tense as well as the negative auxiliary ～ない. However, it does not follow polite forms as politeness is marked in it by using either ～ません or the somewhat less polite ～ないです.
| Plain Speech | Polite Speech | |
| Verbs | するかもしれない Might do | するかもしれません するかもしれないです Might do |
| Adjectives | 古いかもしれない Might be old | 古いかもしれません 古いかもしれないです Might be old |
| Adjectival Nouns （ | 簡単かもしれない Might be easy | 簡単かもしれません 簡単かもしれないです Might be easy |
| Nouns （ | 犬かもしれない Might be a dog | 犬かもしれません 犬かもしれないです Might be a dog |
| ～た | 噓だったかもしれない Might have been a lie | 噓だったかもしれません 噓だったかもしれないです Might have been a lie |
| ～ない | 来ないかもしれない Might not come | 来ないかもしれません 来ないかもしれないです Might not come |
Phrases like ひょっとして (by any chance) and もしかしたら・もしかすると・もしかして (perhaps/possibly) frequently accompany かもしれない.
1. 人間が全ての石油を使いきってしまう時が｛訪れる・来る｝かもしれません。
The time may come when man will use up all oil.
2. 前の試験が難しかったなら、今度の試験も難しいかもしれません。
If the previous exam was difficult, the next exam may also be difficult.
3. もしかしたら彼は気が変わるかもしれません。
Perhaps his mind will change.
4. ひょっとすると雨に遭うかもしれません。
Chances are that we’ll encounter rain.
5. セス先生は厳しすぎるかもしれない。
Seth Sensei might be too strict.
6. このレッスンは初級者には難しいかもしれません。
This lesson might be difficult to beginners.
7. ラファエル君が飲み会に行ったら、彼女に怒られるかもしれない。
If Rafael were to go to the drinking party, his girlfriend might get mad at him.
8. 円安がこの先ずっと長引くかもしれないから、今のところ、円をドルに両替しない方がいいと思いますよ。
Since the depression of the yen might last for the foreseeable future, I think it’d be best not to exchange yen for dollars for the time being.
～かもしれない vs ～だろう
Whereas ～かもしれない indicates a 50/50 probability, ～だろう・でしょう is closer to an 80% probability. It, too, is frequently used with adverbs such as ひょっとして, もしかしたら, etc.
Although ～だろう・でしょう are derivates of the copula だ, they do not attach to things in the exact same way. They instead attach to the 終止形 much like how です does, but they differ from です by how they do so with any inflectable word (用言). In the case of nouns and adjectival nouns, you do not double up on it because it still retains its copular meaning – it just exhibits odd morphology.
| ～だろう | ～でしょう | |
| Verbs | 雨が降るだろう It will likely rain | 雨が降るでしょう It will likely rain |
| Adjectives | 高いだろう It will likely be expensive | 高いでしょう It will likely be expensive |
| Adjectival Nouns | 新鮮だろう It[‘s/will be] surely fresh | 新鮮でしょう It[‘s/will be] surely fresh |
| Nouns | 犬だろう It’s most likely a dog | 犬でしょう It’s most likely a dog |
9. 彼はひょっとしてまだ外にいるでしょう。
He might just be outside.
10. ひょっとしたら彼女はここへ来るだろう。
She will possibly come here.
～かもしれないだろう ？？
～かもしれないだろう, at first glance, seems superfluous, but it is occasionally used. In this scenario, ～かもしれない refers to the probability of the situation occurring at hand, and ～だろう rhetorically questions the listener about their recognition of that probability. As such, ～だろう would be more forceful than ～じゃない ・じゃん, which has a lighter tone.
11. 最後かもしれないだろう。
This might be the last (time), you know.
You may also encounter ～だろうが after ～かもしれない to indicate frustration at what the speaker perceives to be a negatively effect on a likelihood that the speaker is banking on, even though it is only a 50/50 chance.
12. もしかしたらあの女、俺達全員を殺して口封じしようとしてくるかもしれないだろうが。
Ugh, that woman could try to kill us all to keep us quiet.
From 伝説の剣士のつくりかた by 派虎衆.
Albeit old-fashioned, the auxiliary verb ～（よ）う which technically creates だろう can be conjugated normally with conjugatable parts of speech, then be followed by ～かもしれない. However, the supposition meaning of this auxiliary is hardly ever used in modern speech.
13. それだけの意味はあろうかもしれない。
It just might have that much meaning.
By 堀辰雄.
～のかもしれない
By inserting the nominalizer の, the speaker is envisioning a purely hypothetical scenario based on a given truth or the current circumstance. In doing so, the speaker highly emphasizes their opinion on how true that outcome might be, but this is more so on what they are betting on rather than suggesting a higher probability. ～のかもしれない may be used with any tense as well as positive and negative sentences.
| With… | |
| Verbs | 降るのかもしれない It just might rain |
| Adjectives | 新しいのかもしれない It might just be new |
| Adjectival Nouns | 新鮮なのかもしれない It might just be fresh |
| Nouns | 犯人なのかもしれない Might just be the criminal |
| ～ない | 来ないのかもしれない Might just not come |
| ～た | 死んだのかもしれない Just might have died |
Grammar Notes:
By inserting の, notice that the copula in the form of な must be used with nouns and adjectival nouns in the non-past tense.
Contracting の to ん in this grammar point is not seen in standard speech.
14. まだ家へ帰っていなかったのかもしれない。
He might have not been home yet.
15. もしかしたら暑さに負けずに外に出ていたら、何か素敵なことが起きていたのかもしれない。
Perhaps if I hadn’t let the heat get to me and gone out, something fantastic might have happened.
16. 自分が本当にやりたかったことに気がついていなかったのかもしれない。
I might not have ever realized what I truly wanted to do.
17. 健太君が帰ってこないね。もしかしたら事故に遭ったのかもしれない。
Kenta hasn’t come home yet. Maybe he got into an accident.
～やもしれぬ・～やもしれず
The use of the bound particle や is rarely seen in Modern Japanese – largely restricted to the phrase や否や (no sooner than) and the occasional rhetorical phrase such as いつぞや (when was that again? → some time ago). Here, it functions just as か does. As a whole, ～やもしれぬ・やもしれず is quite old-fashioned, with some speakers opting to make it less archaic by using ～やもしれない, but it is nonetheless largely restricted to 時代劇-like speech.
As for when to use ～ず over ～ぬ, this relies on how linguistically pure the speaker wishes to be. Using the 連体形 – ぬ – over the 終止形 – ず – has been true not just for this auxiliary but for all inflectional words for centuries. Furthermore, as is still technically the case in Modern Japanese, sentence endings (語尾) may choose one base over the other, in which only one form would be grammatical. Suffice to say, there is no distinguishable difference between the two iterations in sentence-final position.
18. 賛否両論あるやもしれぬ。
There might be mixed reception.
19. 午後は氷雨やもしれず。
There might be sleet in the afternoon.
～かも
In casual speech, ～かもしれない is frequently contracted to ～かも. What is so peculiar about this contraction is that it loses its ability to be followed by conjunctions and most final particles – with exception to ね・な.
To combat this problem, the copula だ may follow it so that it can then be followed by endings such as ～が・けど・ぞ, etc. You may even see ～かもです, which is not quite as accepted but is gaining currency among younger speakers. However, the use of だ・です after かも is still not so common, but that is likely to change in the coming decades.
20. 彼はもう帰ったかもな。
He might have already come home.
21. それ、いいかも！
That sounds good!
22. いけるかも！
That might work!
23. お金がちょっと足りねーかも。
I might be a little short on money.
24. 来週なら空いてるかも！
I might be free next week!
25. ひょっとして、俺、世界で一番かわいい猫かもにゃあ！
I might just be the cutest cat in the world!
26. 昨日はゴミ収集車が来なかったのかも。
The garbage truck might not have come yesterday.
27. スマホは不幸の原因かもだぞ！
Your smartphone might be the cause of your unhappiness!
28. あんたにとっては、些細なことかもだけどな、俺には重大な問題だぞ。
For you, it may like be trivial, but to me, it’s a big deal!
29. 今なら勝ち目があるかも（だ）よ！
There might be a chance of winning now!
Grammar Note: Although ～よ may directly follow ～かも, the lack of だ causes the sentence to sound feminine.
～かもしれん
You may also encounter the casual variant ～かもしれん, which is most common in male speech or in certain regions where the contraction ～ん for ～ない is prevalent.
30. なるほど、君のいう通りかもしれんね。
Well then, you may be right.
31. 実は他の同僚も俺らの会話聞いてたかもしれんぞ。
Actually, other co-workers might’ve been listening to our conversation, too!