たら: The Versatile If/When | Japanese Grammar

Japanese has four conditionals — と, ば, たら, and なら — where English gets by with a single if. Of the four, 〜たら is the workhorse: it is the one you can reach for when you are not sure which to use, and be right most of the time. This page shows you how to build it, what it means, and — most importantly — why it is so much freer than the other three.

Here is the one fact that unlocks たら: it is just the plain past form with ら stuck on the end. If you already know that 行く becomes 行った and 食べる becomes 食べた, then 行ったら and 食べたら cost you nothing new. The past-tense sound-changes you already learned do all the work.

How to form 〜たら

Take the plain past (〜た for most verbs, 〜だ for the ぬ・ぶ・む and が godan verbs) and add ら. That is the entire rule — every verb, adjective, and noun follows it.

Word	Plain past	たら-form
行く (to go)	行った	行ったら
食べる (to eat)	食べた	食べたら
飲む (to drink)	飲んだ	飲んだら
する (to do)	した	したら
来る（くる） (to come)	来た（きた）	来たら（きたら）
高い (expensive)	高かった	高かったら
静か（な） (quiet)	静かだった	静かだったら
学生 (student)	学生だった	学生だったら

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If you can make the plain past, you can make たら. There is no separate conjugation to memorize — 〜た + ら for everything, 〜だ + ら for the verbs whose past ends in だ. This is why たら is often the first conditional learners can produce reliably.

東京に着いたら、メールするね。

Tōkyō ni tsuitara, mēru suru ne

When I get to Tokyo, I'll email you.

安かったら買うけど、たぶん高いよ。

yasukattara kau kedo, tabun takai yo

I'll buy it if it's cheap, but it's probably expensive.

Two readings: "if" and "when/after"

English speakers expect a conditional to mean if, and often stop there. But たら does double duty. It marks both a genuine hypothetical (if it happens) and a definite future sequence (when / once / after it happens). Which reading you get depends on how certain the event is.

When the event is uncertain, たら is if:

もし宝くじが当たったら、何を買う？

moshi takarakuji ga atattara, nani o kau?

If you won the lottery, what would you buy?

The word もし ("if, supposing") is optional but signals that we are firmly in hypothetical territory. When the event is something you fully expect to happen, the same たら means when or after:

授業が終わったら、電話してね。

jugyō ga owattara, denwa shite ne

When class is over, give me a call.

お母さんが帰ってきたら、ご飯にしよう。

okāsan ga kaette kitara, gohan ni shiyō

When Mom gets home, let's have dinner.

Class will end; Mom will come home. There is no doubt about whether — only when. English forces you to switch words here (if → when), but Japanese leaves たら unchanged and lets context carry the certainty. This is the single most common thing English speakers under-use: たら is not just "if," it is also the everyday way to say "once X happens, (then) Y."

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A useful mental gloss for たら is "once…" rather than "if." "Once I get to Tokyo," "once class ends," "once Mom's home" fits both the certain and the uncertain readings, and it captures the built-in sense of sequence that たら always carries: the たら-event comes first, the main clause follows.

Why たら is the free one: the main clause can be anything

Here is the deep reason たら is the default. The other conditionals restrict what can appear in the main clause. と rejects commands, requests, invitations, and statements of your own will — you cannot say 押すと開けてください. ば resists them too when the subject stays the same. たら imposes almost none of these restrictions. After たら you can put a request, a command, an invitation, or a statement of intention, and it all sounds natural.

Requests and commands (〜てください, 〜て, imperatives):

駅に着いたら電話してください。

eki ni tsuitara denwa shite kudasai

When you arrive at the station, please call me.

分からなかったら、遠慮なく聞いてください。

wakaranakattara, enryo naku kiite kudasai

If you don't understand, please don't hesitate to ask.

Invitations and volitional (〜ましょう, 〜よう):

宿題が終わったら遊ぼう。

shukudai ga owattara asobō

Once your homework's done, let's play.

週末、天気がよかったら海に行こう。

shūmatsu, tenki ga yokattara umi ni ikō

If the weather's nice this weekend, let's go to the beach.

Your own intentions and plain statements:

雨が降ったら行かない。

ame ga futtara ikanai

If it rains, I'm not going.

時間があったら、手伝ってくれる？

jikan ga attara, tetsudatte kureru?

If you have time, could you help me out?

Try mentally swapping と or ば into any of these and you will feel the friction — 駅に着くと電話してください is wrong, 時間があれば手伝ってくれる is stiff. たら takes them all in stride. That flexibility is exactly why teachers tell beginners: when you don't know which conditional to use, use たら. You will rarely be wrong.

The negative: 〜なかったら

The negative conditional is built the same way — from the plain past negative 〜なかった, add ら to get 〜なかったら ("if…not / unless").

この薬を飲まなかったら、熱が下がらないよ。

kono kusuri o nomanakattara, netsu ga sagaranai yo

If you don't take this medicine, your fever won't go down.

明日晴れなかったら、ピクニックは中止です。

ashita harenakattara, pikunikku wa chūshi desu

If it doesn't clear up tomorrow, the picnic is cancelled.

One special use: the "discovery" たら

There is a second, quite different life of たら. When the main clause is in the past tense, たら stops being a condition at all and becomes a report of something you discovered upon acting: 家に帰ったら誰もいなかった ("when I got home, there was no one there"). This is not "if I went home" — both events really happened, and the main clause tells you what you found. Because it behaves so differently, it gets its own page: see たら for discovery and unexpected results. For now, just register that a past main clause after たら means "and then I found that…," not "if."

窓を開けたら、雪が降っていた。

mado o aketara, yuki ga futte ita

When I opened the window, it was snowing.

How たら fits with the other three

たら is the flexible middle ground, but it is not always the best choice — just the safest. If the result is an automatic, mechanical consequence ("push it and it opens"), と is sharper. If you are reacting to something the other person just said ("if you're going to Japan…"), なら is the natural fit. If you want a general, hypothetical "if" without the sense of sequence, ば often reads better. The full side-by-side comparison — with the same idea run through all four forms — lives on と / ば / たら / なら compared, which is the page to read once you can build each form.

Common mistakes

❌ 駅に着くと電話してください。

eki ni tsuku to denwa shite kudasai

Incorrect — と cannot take a request in the main clause.

✅ 駅に着いたら電話してください。

eki ni tsuitara denwa shite kudasai

When you arrive, please call me. (たら freely allows a request.)

❌ 時間があるたら、手伝って。

jikan ga aru tara, tetsudatte

Incorrect — たら attaches to the past form, not the dictionary form.

✅ 時間があったら、手伝って。

jikan ga attara, tetsudatte

If you have time, help me out. (ある → あった → あったら.)

❌ 高いたら買わない。

takai tara kawanai

Incorrect — an い-adjective must go to its past form first.

✅ 高かったら買わない。

takakattara kawanai

If it's expensive, I won't buy it. (高い → 高かった → 高かったら.)

❌ 暇だたら、遊びに来て。

hima da tara, asobi ni kite

Incorrect — a な-adjective/noun needs the past copula だった.

✅ 暇だったら、遊びに来て。

hima dattara, asobi ni kite

If you're free, come hang out. (暇だ → 暇だった → 暇だったら.)

❌ 食べるら、歯を磨いて。

taberu ra, ha o migaite

Incorrect — there is no 〜るら; the base is the past 食べた.

✅ 食べたら、歯を磨いて。

tabetara, ha o migaite

After you eat, brush your teeth. (食べる → 食べた → 食べたら.)

Key takeaways

Form: plain past + ら. 行った → 行ったら, 食べた → 食べたら, 高かった → 高かったら, 静かだった → 静かだったら. No new conjugation.
Meaning: both if (hypothetical) and when / once / after (definite future sequence). Gloss it as "once…" and both readings fit.
The superpower: the main clause can be a request, command, invitation, or statement of intention — the freedom the other conditionals lack.
Default rule: when you are unsure which conditional to use, たら is usually right.
Watch for: a past main clause flips たら into the discovery reading, which is "when I…, I found that…," not "if."

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