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…と: Constant Results and Actual Conditions

The function is to express constant results. The conjugation is just to attach the plain (dictionary) form to と. When you use nouns and na-adjectives, you need to attach だ like 春だと. By constant results, we mean that it’s an unchanged fact, when you do A, aways B happens. You can use this for natural phenomenons, habitual actions, programmed actions, etc.


雨が降ると涼しくなります。
ame ga furu to suzushiku narimasu.
If [it] rains, [it] will get cool.

まっすぐ行くと、郵便局があります。
massugu iku to yuubinkyoku ga arimasu.
If you go straight there is a post office.

…ば: Hypothetical Conditions

The function is to express hypothetical conditions like if a hypothesis comes true, X will happen. This indicate that you place priority on the conditional clauses rather than the main clauses.

薬を飲めば治ると思います。
kusuri o nomeba naoru to omoimasu
[I] think [I] will recover if [I] take the medicine.

夏になれば、海に行きたいです。
natsu ni nareba umi ni ikitai desu
I want to go to the beach when it's summer


…たら: One-Time Results

The function is to express a one-time or a particular result. This has the widest usage and thus we can say たら is most common to express conditionals. The conjugation is to attach ら to the ta-form. By using this, you can express both actual and hypothetical condition.

夏が来たら日本に行きます。
natsu ga kitara nihon ni ikimasu.
If the summer comes, [I] will go to Japan.

薬を飲んだら治ると思います。
kusuri o nondara naoru to omoimasu
[I] think [I] will recover if [I] take the medicine.

…なら: Contextual Conditions

The function is to respond to someone in a given context. Regarding the other conditional words, you can set a context by yourself. However, you can use …なら only when given a context.  The conjugation is just to attach なら to the plain (dictionary) form or the ta-form, which is the only one case that you can attach conditional words to the two forms. 

日本語を話すことができる人がいますか？
nihongo o hanasu koto ga dekiru hito ga imasu ka?
Is there a person who can speak Japanese?

日本語ならトムさんが話すことができますよ！
nihongo nara tomu san ga hanasu koto ga dekimasu yo!
If [you’re talking about] Japanese, Tom can speak [it].

日本語の本を読みたいです。
nihongo no hon o yomitai desu
[I] want to try to read Japanese book.

読みたいなら私のを貸しましょうか？
yomitai nara watashi no o kashimashou ka?
If [you] want to read, shall [I] lend mine?


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