たら

たら means "if": when the first thing happens, the second follows. It is ら added to the plain past – たべたら食べたら, やすかったら安かったら, がくせい学生だったら, いかなかったら行かなかったら – but the た does not make it past. いったら行ったら is "if I go", not "if I went".

The second half can be anything – a request, an invitation, what you intend to do. That makes たら the safest conditional in conversation.

"When" and "after"

If the first thing is sure to happen, たら means "when" or "once": first A, then B.

A always comes first. にっぽん日本にいったら行ったら、かめらカメラをかう買う means buying the camera once you are in Japan; to buy it before you leave, say にっぽん日本にいく行くまえに前に.

たら, と, ば and なら

The four overlap, but they are not interchangeable. と is for what always follows – nature, machines, directions – and cannot end in a request or an intention. たら can.

• × 駅に着くと、電話してください → 駅に着いたら、電話してください

ば puts the weight on the condition: what it takes for B to happen. なら picks up something just said or assumed, and what it introduces can come before the condition is met.

Usage notes

These go beyond conditions about the future.

Finding out what happened

With the second half in the past, たら tells what you found, or what happened, when you did something. Both events really took place, and the second was outside your control. と can do the same, mostly in stories; ば and なら can't.

If the second half is something the same person chose to do next, link the two with the て-form instead.

• × 家に帰ったら、テレビをつけた → 家に帰って、テレビをつけた

Things that didn't happen

With のに or a guess about the past, たら imagines what would have happened if things had gone differently. わたくし私だったら is "if it were me".