The たら Conditional: Once X Happens, Then Y

The たら conditional attaches ら to the plain past (ta-form) of a predicate. It is the broadest, most forgiving conditional in Japanese, and the one that allows a command or request in the result clause.¹ It does two main jobs: it states a condition ("if / once X happens, then Y") and it reports a discovery ("when I did X, I found Y").¹²

Overview

たら marks the condition that the main clause depends on, with the sense "if/when X is completed, then Y."¹ Because the form is built on the past tense, the condition is framed as realized or finished before the result follows.¹

What たら does

The second clause always follows the first in sequence. たら frames its condition as completed before the result, then states what is done once that condition is met.¹

The tense of the whole sentence is set by the second (main) clause, not by the た in the condition. The past-form base does not by itself make the sentence past.¹³

Because たら "merely shows that when one condition or action is completed then the second is done, regardless of whether it is factual or not," it can read as either "if" or "when" depending on context.¹ English speakers feel these as different ideas, but たら itself does not distinguish them.¹

たら is the default conditional when you are unsure which to use. It accepts essentially any clause type in the result position, which is why learners reach for it first.⁴⁵

The condition is mentally "done" first

Because たら is literally the plain past plus ら, the condition is framed as already completed: read it as "once it's done, then Y." That mental picture matches the rule that the second clause always follows the first sequentially.¹

Register and JLPT placement

たら is neutral in register and common in both speech and writing. In speech, it is the go-to form for "if/when."⁵⁶ The connective itself is plain: politeness lives in the main-clause ending, not in たら. A 〜たら…ください sentence is polite, while 〜たら…しろ is a blunt imperative. The たら is identical in both.¹⁵

A polite conditional variant, でしたら, exists for nouns and na-adjectives. It is a more formal counterpart of だったら used in service and keigo (honorific-language) contexts.³

Recognized graded references place the pattern at JLPT N4.⁵⁶ It assumes you already know the plain past (ta-form), itself an N5/N4 milestone, so N4 is the standard placement.⁵⁶

How to form たら

The rule is the same across every word class: take the plain past and add ら. Once you can build the plain past of a word, you can build its たら form.¹³

Verbs: plain past + ら

Take any plain past (ta-form) and add ら. Because the rule uses the existing ta-form, every ta-form sound change carries over automatically.¹³

Affirmative: 食べる → 食べた → 食べたら; 行く → 行った → 行ったら.³ Negative: 食べない → 食べなかった → 食べなかったら.³

先生せんせいが来きたら、こんばんはとちゃんと挨拶あいさつしてね。¹
"When the teacher comes, be sure to greet him properly with 'good evening.'"

一口ひとくち食たべたら、きっと好すきになるよ。⁵
"Take one bite and you'll surely come to like it."

ご飯ごはんができたら呼よんで。⁷
"Call me once dinner is ready."

い-adjectives: かったら

Drop the final い, add かった, then ら. This is just the い-adjective plain past plus ら.³⁶

Affirmative: 高い → 高かった → 高かったら; 寒い → 寒かったら.³ Negative: 高くない → 高くなかった → 高くなかったら ("if it isn't expensive").³

辛からかったら、牛乳ぎゅうにゅうを飲のんでください。⁶
"If it's spicy, please drink some milk."

お茶ちゃの味あじが薄うすかったら、言いってください。⁶
"If the tea tastes weak, please tell me."

な-adjectives and nouns: だったら

Add だった, then ら, to a na-adjective stem or a noun. This is the plain past of the copula plus ら.³⁶

Na-adjective: 静か → 静かだった → 静かだったら; 暇 → 暇だったら.⁵⁶ Noun: 雨 → 雨だった → 雨だったら; 週末 → 週末だったら.⁶ Negative: 〜じゃなかったら, for example 不安じゃなかったら.³ The polite variant でしたら appears in formal speech, for example 雨でしたら.³

暇ひまだったら、手伝てつだってください。⁵
"If you're free, please help me out."

週末しゅうまつだったら、時間じかんありますよ。⁶
"If it's the weekend, I have time."

Negative and past-of-past notes

なかったら is the negative conditional ("if not"): it is simply the plain-past negative (〜なかった) with ら attached, with no special rule.³

The ら attaches to whatever plain-past stem comes before it across all word classes (verb なかった, い-adjective 〜くなかった, na-adjective/noun 〜じゃなかった). Once you know the plain past, the conditional is automatic.³

もし食たべに行いきたかったら、行いこう。⁶
"If you want to go out to eat, let's go."

歯はが痛いたいんだったら、歯医者はいしゃさんに行いったら？⁷
"If your tooth hurts, why not go to the dentist?"

もし is an optional flag, not part of the form

Placing もし at the head of the clause signals the hypothetical "if" reading, but it is optional and does not change the conjugation.⁶

Meaning and usage contexts

"If": the hypothetical, one-time condition

たら typically frames a specific, often one-time condition the speaker is not certain will occur. This contrasts with と, which frames a general, automatic, or habitual relationship ("whenever X, Y").⁴

One source labels the split directly: たら gives "one-time results" while と gives "constant results."⁴ Compare 一時になったら出発しよう ("when it gets to one o'clock, let's leave," a single specified occasion) with 雨が降ると涼しくなる ("when it rains, it gets cool," an automatic, recurring phenomenon).⁴

時間じかんがあったら観光かんこうしたいです。⁴
"If I have time, I'd like to do some sightseeing."

お金かねがあったら、留学りゅうがくする。³
"If I had the money, I'd study abroad."

"Once / when": the realized future condition

When the speaker treats the condition as something that will be completed, たら reads "once / when X is done, then Y." The completion nuance is built into the past-form base: た frames X as finished before Y begins.¹

This is the realized, time-sequence reading, kept brief here. The pure "when, not if" sequence use has its own dedicated treatment elsewhere in the pillar.

春はるが来きたら旅行りょこうに行いこう。⁷
"Once spring comes, let's go on a trip."

掃除そうじが終おわったらマッサージしてね。⁷
"When you finish cleaning, give me a massage, OK?"

The result clause: たら's signature freedom

This is the heart of たら. The form freely permits a volitional or non-declarative main clause: commands, requests, invitations, suggestions, and the speaker's own intention. と and ば have restrictions here. たら does not.⁸¹⁴

と is restricted because it links two events as an automatic, natural sequence. As a result, "the second and main clause cannot be volitional or controllable. In other words, you can't finish the sentence with 'I will [verb],' or 'Please [verb].'"¹ A と clause expressing the speaker's own intended action is read as unnatural.⁴

ば is restricted differently. When the ば clause contains an action verb, the main clause "cannot have any volition such as command, request or definite expression of volition." If a volitional verb is used anyway, it gets reread as something that happens automatically.¹ The exception: when the ば clause is a state (a stative verb like ある, an adjective, or a potential form), the main clause's volition is freely allowed. Examples include お金があれば、旅行したい and 寒ければ暖房をつけてください.¹⁴

たら carries no such restriction. The result clause may use any tense or mood: volition, desire, command, request, or suggestion. This is true whether the condition is an action or a state.⁴⁵

飲のんだら運転うんてんするな。⁴
"If you've been drinking, don't drive."

よかったら手伝てつだってくれませんか？⁴
"If it's all right, could you help me?"

日本にほんへ行いったら、たくさん写真しゃしんを撮とろう。¹
"When I go to Japan, let's take lots of photos."

Why と fits automatic outcomes

と is licensed only for non-volitional results, which is exactly why it suits habitual truths and automatic sequences, where たら would wrongly imply a single, specified occasion.⁴

The discovery / perception use (たら-perception)

Action, then discovered state

In the discovery use, clause 1 is the speaker's action and clause 2 is a state that the action revealed. Clause 1 is always an action, and clause 2 must be a state. Clause 2 cannot be a further action.²

This is not a conditional at all. Here たら means "when I did X, I found Y," reporting a discovery rather than setting up a condition.¹² Clause 2 frequently ends in 〜ていた / 〜ていました, a state already in progress. That ending makes the sentence read as a pre-existing situation the speaker walked into.²

ドアを開あけたら、大おおきい犬いぬがいました。²
"When I opened the door, there was a big dog."

カーテンを開あけたら、雨あめが降ふっていました。²
"When I opened the curtain, it was raining."

郵便受ゆうびんうけを開あけたら、友達ともだちからの手紙てがみが来きていました。²
"When I opened the mailbox, a letter from my friend had arrived."

Why the main clause is past tense

The past tense in clause 2 forces the realized "when I did X, I found Y" reading: the situation was already true and the action merely uncovered it.¹²

The discovery is non-volitional and typically a mild surprise. When たら is used this way, the main clause "must express some sort of surprise and must be out of the speaker's control." It is almost as if, after the たら, the speaker pauses and says, "and then guess what happened, Y."¹ The past tense reflects that what happened next was unexpected.²

日本にほんへ行いったら、皆みんな日本語にほんごを早はやく話はなすのでびっくりした。¹
"When I went to Japan, I was surprised at how fast everyone spoke."

窓まどの外そとを見みたら、彼かれが立たっていた。⁷
"When I looked outside the window, he was standing there."

Discovery is unique to たら

The "I found out" reading belongs to たら alone among the four conditionals. と, ば, and なら do not produce this discovery use.²

たら against と and ば

Quick contrast table

The three conditionals differ along three axes: the kind of condition they frame, what they allow in the result clause, and their register. The result-clause column is where たら stands apart from The と Conditional and The ば Conditional.

Form	Condition type	Result-clause restriction	Register	Typical translation
たら	Specific, often one-time; condition treated as completed before the result.14	None: commands, requests, invitations, suggestions, and the speaker's intention are all allowed.14	Neutral; spoken go-to, politeness set by the main-clause ending.15	"if / once / when (X is done), then Y"
と	General, automatic, habitual; "whenever X, (inevitably) Y."14	Strong: no commands, requests, or volitional/controllable results ("I will…" / "Please…" not possible).1	Neutral; common for natural laws and machine-like outcomes.1	"whenever / when X, Y (automatically)"
ば	Hypothetical or logical supposition.1	With an action-verb condition, no command/request/volition in the main clause; volitional verbs get reread as automatic. Exception: if the condition is a state (stative verb, adjective, potential), volition is freely allowed.14	Somewhat formal; frequent in idioms (なければならない).1	"if X (were the case), Y"

When to reach for たら

When you are unsure which conditional to use, default to たら. It overlaps と and ば across most "if/when" situations. It is also the only one of the three that licenses a request, command, or volitional result clause without these restrictions.⁴⁵

Use と instead when the relationship is an automatic, always-true, or habitual consequence. In that setting, a one-off たら would sound like a single occasion.¹⁴

Use ば for hypothetical or logical suppositions and set idioms. But if you need a request or command in the result and the condition is an action, switch to たら.¹

Good to know

ら rides on the past form, so the condition is "done" first

Because たら is literally the plain past plus ら, the condition is framed as completed before the result. Think "once it's done, then Y." This matches the rule that the second clause must always follow the first sequentially.¹

Using たら for an always-true automatic result

For a recurring natural phenomenon, たら sounds like a single specified occasion. と reads as the natural choice. A one-off framing like 一時になったら出発しよう fits たら because it names a single moment, but a constant, always-true relationship wants と.⁴

雨あめが降ふると涼すずしくなる。⁴
"When it rains it gets cool."

Putting a request or command after と or after an action-verb ば

A request result cannot follow と. It also cannot follow ば when the ば clause is an action verb. Writing 駅に着くと、電話してください is incorrect because と forbids a volitional or controllable main clause. たら carries no such restriction, so the request attaches freely.¹⁴

駅えきに着ついたら、電話でんわしてください。¹
"When you arrive at the station, please call."

〜たらどう(ですか) for a gentle suggestion

A たら clause followed by どう(ですか) softens advice into "why don't you…? / how about…?," as in 歯医者さんに行ったら(どう)？.⁷⁵ The related 〜たら…いい(ですか) likewise marks suggestion or permission ("you'd best…" / "should I…?").¹ Recognize the pattern when you meet it. The softener is not this article's focus.

See also

• Japanese Conditionals Overview: と, ば, たら, なら (Which "If" to Use)
• The と Conditional: Natural and Automatic Consequences
• The ば Conditional: The Hypothetical "If"
• The なら Conditional: "If You're Talking About"
• When Conditionals Don't Mean "If": The Sequence Use of と and たら
• Counterfactual Conditionals in Japanese: ば…のに and たら…のに

References

Footnotes

1. Chapter 10: If Clauses (と / ば / なら / たら conditionals). Mikuni International School. https://mikuniinternational.org/wp-content/uploads/2021/04/Chapter-10-Conditionals.pdf ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²² ↩²³ ↩²⁴ ↩²⁵ ↩²⁶ ↩²⁷ ↩²⁸ ↩²⁹ ↩³⁰ ↩³¹ ↩³² ↩³³ ↩³⁴ ↩³⁵ ↩³⁶ ↩³⁷ ↩³⁸

2. Learn Japanese Adventure. "たら (tara) Sentence for Discovery." https://www.learn-japanese-adventure.com/tara-sentence-discovery.html ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰

3. Tofugu. "Japanese Conditional Form たら." https://www.tofugu.com/japanese-grammar/conditional-form-tara/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵

4. 4946 Wasabi. "How Conditionals Work in Japanese." https://wasabi-jpn.com/magazine/japanese-grammar/how-conditionals-work/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹

5. JLPT Sensei. "JLPT N4 Grammar: たら (tara) Meaning." https://jlptsensei.com/learn-japanese-grammar/たら-tara-meaning/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹²

6. Bunpro. "たら (JLPT N4)." https://bunpro.jp/grammar_points/たら ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹²

7. Maggie Sensei. "Conditional: 〜たら = ~tara." https://maggiesensei.com/2011/02/17/conditional-%e3%80%9c%e3%81%9f%e3%82%89-tara-request-lesson/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

8. Makino, Seiichi, and Michio Tsutsui. A Dictionary of Basic Japanese Grammar. The Japan Times, 1989. ↩