もし

adverb

if; in case

descriptive

1. if; in case

Introduces a hypothetical condition, typically used with conditional forms like ～たら or ～ば.

もし雨(あめ)が降(ふ)ったら、行(い)きません。

If it rains, I won't go.

もし時間(じかん)があれば、手伝(てつだ)ってください。

If you have time, please help me.

もしよかったら、一緒(いっしょ)に行(い)きませんか。

If you'd like, would you like to go together?

Polite invitation

もし明日(あした)天気(てんき)がよかったら、公園(こうえん)でお弁当(べんとう)を食(た)べませんか。

If the weather is nice tomorrow, shall we eat boxed lunches in the park?

もし日本(にほん)に住(す)むことになったら、どこに住(す)みたいか考(かんが)えたことがありますか。

Have you ever thought about where you would want to live if you were to live in Japan?

もし marks a hypothetical condition and is typically paired with conditional forms.

Common patterns

もし〜たら: if ~ (most common, neutral)
もし〜ば: if ~ (slightly formal)
もし〜なら: if ~ (topical, "speaking of")
もし〜としたら: supposing that ~

Common expressions

もしよかったら: if you'd like (polite offer)
もし何(なに)かあったら: if something happens
もし可能(かのう)なら: if possible

Usage

もし is an adverb, so it appears before the condition, not after.
もし is optional—conditionals work without it. Adding もし signals from the start that a condition is coming and stresses that it is hypothetical.

雨(あめ)が降(ふ)ったら... = If it rains...
もし雨(あめ)が降(ふ)ったら... = If (by any chance) it rains...

Related Words

Related: もしも (emphatic form)

Related: 仮(かり)に (supposing, hypothetically)

Compare: 例(たと)え (example)

core

Added 2026.1.8 12:55 · Revised 2026.10.9 4:34

01000/01284_moshi