〜たら vs 〜ば

〜たら is a conversational conditional indicating sequential progression ("when/once X happens, then Y") and naturally allows requests, invitations, and commands in the following clause. 〜ば is a logical conditional focusing strictly on the prerequisite condition needed for an outcome ("provided that X is met, then Y"), and cannot be followed by direct requests or commands. Swapping たら to ば makes the statement more formal and analytical while forbidding imperative or requesting conclusions.

〜たら if; when (after)

駅(えき)に着(つ)いたら、電話(でんわ)をかけてください。

When you arrive at the station, please give me a call.

暇(ひま)だったら、一緒(いっしょ)に映画(えいが)を見(み)に行(い)きませんか。

If you are free, won't you go see a movie with me?

〜ば if (conditional)

安(やす)ければ、その靴(くつ)を買(か)いたいです。

If it is cheap, I want to buy those shoes.

毎日(まいにち)練習(れんしゅう)すれば、上手(じょうず)に話(はな)せるようになります。

If you practice every day, you will become able to speak fluently.