Ba ば

Particle meaning: if, when.

1. Used in ba-form of verb

あそこに行けば山田さんに会えます。

Asoko ni ikeba yamada san ni aemasu.

If you go over there, you can see Mr. Yamada.

もっと早く来ればよかった。

Motto hayaku kureba yokatta.

If I had come much earlier, it would have been better. (I should have come much earlier.)

彼女が来れば教えてください。

Kanojo ga kureba oshiete kudasai.

When she comes, please tell me.

(for a future condition, <no> nara is used instead of ba after dictionary form of verb)

東京に行くのなら新幹線がいいですよ。

Toukyou ni iku no nara shinkansen ga ii desu yo.

If you’re going to Tokyo, you should take the shinkansen.

2. After (adjective) noun + nara (conditional form of da)

明日雨ならば行きません。

Ashita ame naraba ikimasen.

I won’t go if it is rainy tomorrow.

3. Used in ba-form of adjective

よろしければどうぞ食べてください。

Yoroshikereba douzo tabete kudasai.

If it is all right (If you feel like it), please eat.

-> See also nara, tara, to, to sureba, Adjective Forms (II)