Conditional 〜たら: The Most Versatile 'If/When' in Japanese

The "if" and the "when" it carries

〜たら is the conditional you'll reach for most often. Depending on context it means "if" or "when": "if it rains, I'll stay home" or "when I finish, I'll call you." What ties the two readings together is that the second clause hasn't happened yet — たら sets up something that follows once the first thing is true. That one form stretches across hypotheticals, one-time future sequences, and even surprising discoveries about the past, which is why it's the most versatile of Japan's four main conditionals (たら, ば, と, なら).

Building it: plain past + ら

The formation is wonderfully simple: make the plain past (the た-form), then add ら. If you already know the た-form, you're done — every word type works the same way.

Because it's built straight from the past tense, the same sound changes you already know apply: 行く → 行った → 行ったら, 飲む → 飲んだ → 飲んだら. Two habits keep it accurate: attach ら to the plain past, never the dictionary form (食べたら ✓, not 食べるたら ✗), and keep the だった on nouns and な-adjectives — it's 学生だったら and 静かだったら, since the だった is part of the past form.

When it reads as "if," and when as "when"

When the first clause is a condition that may or may not happen, たら means "if," and the optional word もし ("if, supposing") often sits at the front to flag the hypothetical:

When the first clause is instead something that will happen, with the second following it, たら shifts to "when" — first this, then that:

Where たら pulls ahead: requests, commands, and discoveries

This is たら's real advantage over its rivals, and the clearest sign of how far its reach extends. The ば and と conditionals resist a request or command in the second clause, but たら welcomes one freely. So whenever you want "when X happens, please do Y," たら is the natural — often the only — choice:

There's one more flavor the others can't match: when both clauses are in the past, たら can report a discovery — you did one thing and then found something unexpected. It still means "when," now with a note of surprise:

たら next to ば, と, and なら

Because たら is so flexible, the practical skill is knowing where the other three would break:

• と and ば before a request. "When you get there, call me" needs たら: 着いたら電話して. Saying 着けば電話して or 着くと電話して sounds wrong, because と and ば resist commands and requests.
• たら vs なら. なら responds to a topic someone just raised ("if you mean sushi, that shop is good"), while たら is for an actual event or condition that will or could occur. They aren't interchangeable.

For a side-by-side look at all four conditionals, see 〜と / 〜ば / 〜たら / 〜なら compared.

The short version

• Build it from the plain past + ら: 行った → 行ったら, 高かった → 高かったら.
• It means "if" (hypothetical) or "when" (a one-time future event), read from context.
• もし often marks the hypothetical "if" reading.
• It's the only conditional that comfortably takes a request, command, or suggestion afterward.
• Past + past たら can signal a surprising discovery: 帰ったら誰もいなかった.

Practice it