もし

もし is an adverb meaning "if" that is placed at the beginning of a conditional clause to emphasize the hypothetical nature of the situation. It signals to the listener early on that a supposition is coming, and it is almost always paired with a conditional ending such as 〜～たら, 〜～ば, 〜～なら, or 〜～と.

While the conditional endings themselves already convey "if," adding もし makes the hypothetical feeling stronger and clearer – especially useful in longer sentences where the listener benefits from an early signal.

もし ～たら

This is the most common pairing. It expresses a concrete hypothetical condition.

もし ～ば

Used for general or logical conditions.

もし ～なら

Used when the condition is based on a situation or assumption.

Usage notes

• もし is optional. The conditional form alone is grammatically complete. もし simply adds emphasis or clarity.
• もし is particularly common in questions and requests, where the speaker is being polite by framing the situation as hypothetical:
  もしよかったら、れんらく連絡してください。

  If it's all right with you, please contact me.
• The set phrase もしもし (used when answering the phone) is derived from もし, but has become a fixed greeting and is unrelated to conditional grammar.