もし

も

し

Common wordJLPTN5Freq.FrequencyTop 1,000

Meanings

usually written using kana alone

Used at the beginning of a conditional clause, often paired with ～たら, ～ば, or ～なら. Marks a hypothetical or uncertain situation.

もし〈事こと〉たらif (something happens), then...
もし雨あめが降ふったら、試し合あいは中ちゅう止しです。
If it rains, the match will be cancelled.
もし〈事こと〉ならif it's the case that... (used for conditions or suppositions)
もし時じ間かんがあるなら、手伝てつだってください。
If you have time, please help me.
もし〈事こと〉場ば合あいはin the event that... (formal conditional)
もし何なにか問もん題だいがあった場ば合あいは、すぐに連れん絡らくしてください。
If there is any problem, please contact us right away.
もし〈事こと〉としてもeven if (something were the case)
もし失しっ敗ぱいしたとしても、諦あきらめません。
Even if I fail, I won't give up.

万まん一いちN3
万一 is a more formal word emphasizing a rare, worst-case possibility, while もし is the everyday, general word for introducing any hypothetical.
仮かりにN1
仮に sets up a hypothetical premise for the sake of argument or discussion, whereas もし is used more broadly for everyday conditional statements.

もしN4
This もし ('excuse me!/hey!') is a homograph of the conditional もし ('if'), and learners must rely on context to tell the interjection from the conjunction.

もしUsage99%
Kana spelling is standard; the kanji form 若し is rare and literary.
若もしUsage1%
Kanji form is occasionally seen in older or formal writing, but kana is strongly preferred.

The historical derivation is uncertain; it has been used as a conditional particle since Old Japanese.