If, When, and Other Uncertainties


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All languages have ways to express conditionals, such as "if it's sunny tomorrow, I'll go swimming," "when it rains, my car leaks," or "in Tom's case, reading was a chore."

But Japanese makes these constructions into true art forms. Japanese has dozens of ways of expressing uncertainty, conditionals, and other ideas that are not direct statements. As a consequence, it is never straightforward just to say "if" or "when" in Japanese. Each expression has different implications, and you must choose the right one if you are to be understood.

One key thing to realize is that in Japanese, the verb tense in dependent clauses does not necessarily relate to the tense of the whole sentence. In some of the cases below, the verb tense you choose for the "if/when" clause affects the meaning. Only the final verb in the main clause can make the sentence present or past tense, so don't get hung up on present or past verbs in the dependent clause-- use whichever one conveys the right meaning.

So if you're ready, let's begin. These forms and their usage with -i adjectives, -na adjectives, and nouns are summarized in a table at the end. Please note that this is not a complete list.


Baai really means "case," so it is always hypothetical. It is used where you would say "in case of..." or "in the case that..." in English. Osoku naru baai, renraku shite kudasai means "In case/if it gets late, please call."

It is also used on written forms that ask for the respondent's opinion: Anata no baai,... means "In your opinion...". Baai is a noun.


This one has some subtlety. Toki literally means "time" and functionally means something like "at the time of." [In fact, the kanji for toki is the same as that for ji, meaning "hour" (like 2-ji, 2 o'clock).] It can be hypothetical ("if") or actual ("when"), but is more likely to be used to mean "when".

The subtle part is what verb form to use in front of toki, which is a noun, by the way. Using a past-tense verb means that you have already completed the action in the dependent clause, while using a present-tense verb means the action is not yet complete.

For example, Nihon ni itta toki means "when I went to Japan," and crucially, it implies that the main clause occurred in Japan. (Ie, you have already gotten there). Nihon ni itta toki, tomodachi ni atta means "when I went to Japan, I met a friend (in Japan)." Similarly, Nihon ni itta toki, tomodachi ni au means "when I go to Japan, I will meet my friend (in Japan)." (Or it could mean, "If I were to go to Japan, I would meet my friend there").

So perhaps the best translation of Nihon ni itta toki, although awkward, is "having gone to Japan..."

In contrast, Nihon ni iku toki means "while going to Japan," and it implies that the main clause does not occur in Japan (that is, you are not there yet). Nihon ni iku toki, tomodachi ni atta means you were on your way to Japan, but you met your friend before that-- perhaps on the plane, or in the airport right before you left.

In some cases, baai and toki are interchangeable, such as omoi toki = omoi baai = "if it's heavy...". But note this difference: kodomo no toki means "when I was a child," but kodomo no baai means "in case of children" or "in case you are a child."


Nara is always translated as "if," but the implication is that some assumption is being made by the speaker. You use nara when you are drawing attention to the particular case at hand. Raishuu nara hima desu means "if you're talking about next week, I am free." The idea is often that the condition in the nara clause is the only one required to fulfill the main clause.

Don't use nara for things that are very likely to happen or which require no assumption, such as "If it's warmer this summer than this winter..." In fact, nara is not used very much in speech.


-Te is used in the middle of sentences to connect one action to another. It implies a sequence of events. In some cases, the events are not causal, but in cases where they are, -te can be thought of as a form of conditional. (This is the same -te form as is used for a variety of other forms, like requests and progressive action; it is the same as the -ta form, just using -te instead).

Ano resutoran de tabete byoki ni narimashita literally means "I ate at that restaurant and became sick," but since the implication is that the first one caused the second, a better translation is "When I ate at that restaurant, I became sick."

You'll have to judge from context whether causality is implied in a -te sentence. For instance, tabete dekakemashita ("I ate, then left the house") is not causal.


This usage is extremely common because it's simple, fast, and versatile (it can mean either "if" or "when"). The -tara form is just the simple past-tense verb form (-ta or -da) plus -ra. So iku becomes ittara and yomu becomes yondara. -I adjectives use their simple past, while -na ajectives and nouns take dattara (the simple past form of da).

However, this form also has some subtlety. It's important to understand that -tara expresses completed action. The dependent clause has finished occurring before whatever happens in the independent clause. (Thus, it is similar to the -ta toki form described above).

Furthermore, the meaning differs somewhat depending on the tense of the final verb. A -tara, B -mashita (past tense) means "A occurred, then B happened." It is translated as "when." For example, Mado o aketara, samuku narimashita means, "when I opened the window, I got cold."

But A -tara, B -masu (present/future tense) means that if or when A occurs, B will occur. It is translated as "when" in cases where it is reasonably certain that A will occur, and "if" otherwise. For example, Mado o aketara, samuku narimasu means "if you open the window, I'll get cold" and kuraku nattara, kaeranakereba narimasen means "when it gets dark, I have to return home."

A final note about -tara is that it is preferred in the case of neutral or accidental happenings over the other forms described here. So if you say Kaigi ni ittara, tomodachi ni aimashita, it means that you met your friend at the meeting, and it was either accidental (in which case that sentence can start a conversation-- "Hey! I saw Joan at the meeting!") or neutral (in which case that sentence answers the question, "When did you meet your friend?").

-Tara can also be used for intentional actions, of course-- Tanaka-san ga kitara, shirasemasu ("when Tanaka comes, I'll inform him"). The point is that it is the only form possible for situations out of the speaker's control.

[By the way, all these subtleties should not be thought of as hard-and-fast rules, but merely guidelines for expressing what you really mean. Of course in practice there will be some exceptions.]


Moshi always means "if," and it is not a complete form by itself. It must be used in conjunction with another conditional, usually nara or -tara. It comes at the beginning of the dependent clause.

Moshi can serve a couple of purposes: first, it can be used to emphasize the "hypotheticality" of the situation. Moshi shinu nara means "if I die..." Second, it can be used simply as an "advanced warning" that the dependent clause is going to be conditional. Since Japanese is structured such that you have wait for the end of phrases and clauses to find out what's going on, Japanese people have evolved a few strategies to give clues about what's coming. Moshi is often used in front of long -tara clauses in writing.


To as a conditional has a few meanings. First, it can imply that something occurs as a natural, habitual, or expected result. In some cases, the idea is almost "whenever" instead of "when" or "if." Haru ni naru to hana ga sakimasu means "When spring comes, the flowers bloom."

To is also used to give instructions: Kono botan o osu to oto ga kikoemasu-- "if/when you press this button, you'll hear a sound." Here the sense is one of immediate consequences: as soon as you do this, this other thing will happen.

And finally, it can be used to give the speaker's opinion: Ame ga furanai to ii desu-- "I hope it doesn't rain" [literally, "if it doesn't rain, it's good"].

By the way, to isn't used with sentences whose main clause concerns your own requests or suggestions, or the granting of permission, prohibition, etc. So you can't use to in a sentence meaning "if you can stay for a while, please sit" or "if it stops raining, shall we go for a walk?"


This form means "if" much more often than it means "when." It is often the form called "the conditional form" in grammar texts and is almost always used for hypothetical situations. For regular verbs, replace -u with -eba; for semiregular verbs, replace -ru with -reba; and for kuru and suru, use kureba and sureba. [The corresponding negative forms use the -nai stem: replace -nai with -nakereba.]

-I adjectives inflect like the verbs: replace -i with -kereba for the affirmative, and use -ku nakereba for the negative. -Na adjectives and nouns just take nara or dattara in the affirmative (naraba can be used in writing or formal speech only), and de nakereba in the negative.

This form is very handy for general conditionals. Samukereba, seta o ki nasai means, "if you're cold, put on a sweater." Isogeba, maniau darou means, "if we hurry, we'll probably make it in time."

But there is a restriction on -ba. It's the same as for to above-- you can't use it when the main clause expresses a command, suggestion, permission, or prohibition. However, unlike to, there are a few exceptions for -ba. You can use this form even for suggestions, etc when (1) the conditional is an -i adjective (that's why the above sentence with samukereba is OK), (2) the conditional verb is aru or iru (areba or ireba), and (3) the conditional is negative (-nakereba).

Remember, you can always use -tara. So if you're unsure that a given situation can take -ba or to, just use -tara.

Sometimes Japanese use conditionals in places where we wouldn't do so in English. For instance, the sentence Ano mise ni ikeba, 1,000-yen de kaemasu yo means "you can get it for 1,000 yen at that store" (literally, "if you go to that store, it can be bought for 1,000 yen").

Whew! That's a lot of ways to express conditionals. To reduce some of the uncertainty, I've made this table of how to use each one with -i adjectives (such as hayai), -na adjectives (such as benri(na)), and nouns (such as ame). I've also indicated forms for verbs (iku [regular], taberu [semiregular], kuru and suru) where appropriate.


-i Adjective

-na Adjective


Verb (aff/neg)



hayai baai

benrina baai

ame no baai

plain form for all verbs (eg, iku, itta)

case/in case of/in the case that


hayai toki

benrina toki

ame no toki

plain form (note difference in meaning)

Usually "when," but also "if"; literally means "time" or "at the time of"

with present tense verb: action in dependent clause is not yet complete

with past tense verb: action has been completed


hayai nara

benri nara

ame nara

plain form

"if"-- indicates some assumption on the speaker's part


hayakattara (aff.)
hayakunakattara (neg.)

benri dattara (aff.)
benri de nakattara (neg.)

ame dattara (aff.)
ame de nakattara (neg.)


"if" or "when"-- always expresses completed action.






"if"-- moshi is not complete by itself. It comes before the dependent conditional clause, which then has another conditional form, usually nara or -tara.


hayai to

benri da to

ame da to

plain form

"if" or "when," but almost with the sense of "whenever."

This form cannot be used for suggestions, requests, permission, or prohibition


hayakereba (aff.)
hayaku nakereba (neg.)

benri nara/ benri dattara (aff.)
benri de nakereba (neg.)

ame nara/ ame dattara (aff.)
ame de nakereba (neg.)


Usually "if" but sometimes "when"

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