A grammatical form of verbs or adjectives expressing a hypothetical or conditional meaning ("if ..."). In modern Japanese it corresponds to conditional forms such as the 'ba' or 'tara' constructions.
動詞の仮定形は、文中で条件を示すのに使われます。
The conditional form of verbs is used in sentences to indicate conditions.
『雨が降れば、出かけません』の『降れば』は仮定形の一例です。
The '降れば' in 'If it rains, I won't go out' is an example of the conditional form.
古典文法では仮定形と已然形が区別されますが、現代語では意味が重なることもあります。
Classical grammar distinguishes the conditional form from the 已然形 (realis form), but in modern language their meanings sometimes overlap.