もし — The Hypothetical Marker
An optional adverb placed at the START of a sentence to signal that a hypothetical 'if' is coming. The actual conditional grammar (たら/ば/と/なら) still appears at the end of the clause.
Structure
もし + [Condition + たら／ば／と／なら] + [Result]
Examples
もし雨が降ったら、行きません。
Moshi ame ga futtara, ikimasen.
If it rains, I won't go.
もし (hypothetical signal) + 雨が降ったら (if it rains, たら-conditional) + 行きません.
もし時間があったら、遊びに来てください。
Moshi jikan ga attara, asobi ni kite kudasai.
If you have time, please come over.
もし (hypothetical signal) + 時間があったら (if you have time, たら-conditional) + 来てください.
もし明日晴れたら、山へ行きましょう。
Moshi ashita haretara, yama e ikimashou.
If it's sunny tomorrow, let's go to the mountains.
もし announces the 'if'; 晴れたら (if it clears up) carries the actual conditional grammar.
• Optional: You can drop もし and the たら still means 'if'. もし simply warns the listener early that a hypothetical is coming. • もし pairs with a conditional ending; it does not replace it.
Commonly confused with
The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones もし is tested against.
vs たら／ば／と／なら
Those are the actual conditional verb forms doing the grammatical work; もし is just an optional front-of-sentence flag that can accompany any of them.
vs もしも
もしも is a more emphatic/literary version of もし, stressing an even more remote or dramatic hypothetical.
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