Conditional particle meaning 'if' or 'when' (if ... then); used to form conditional clauses.
雨が降れば、試合は中止です。
If it rains, the game will be cancelled.
時間があれば手伝います。
If I have time, I'll help.
安ければ買います。
If it's cheap, I'll buy it.
Can connect clauses in an additive or parallel way (often seen in patterns like '...も...ば...も'), similar to 'both ... and ...'.
この店は味も良ければ値段も安い。
This shop has good taste and cheap prices as well.
彼は音楽もできればスポーツも得意だ。
He can do music and is also good at sports.
仕事も忙しければ、帰りも遅い。
Work is busy, and he also comes home late.
Sentence-final or short suggestion meaning 'why don't you ...?' used colloquially (e.g., '行けば？').
早く寝れば？
Why don't you go to bed early?
それ、買えば？
Why don't you buy that?
一緒に行けば？
Why don't you go together?
Used in comparative constructions ('the more ... the more ...'), often in the pattern '...ば...ほど' meaning 'as/when ... increases, ...'.
練習すればするほど上手になる。
The more you practice, the better you become.
食べれば食べるほどお腹がいっぱいになる。
The more you eat, the fuller you get.
使えば使うほど便利になる道具だ。
It's a tool that becomes more useful the more you use it.
Archaic or literary usage meaning 'because' or 'since'; mainly found in classical texts and old-style writing.
彼、若ければこそ勝てり。 (文語・例示)
Precisely because he was young, he won. (literary/example)