If/When Dependencies with たら

There are several ways to express "if" in Japanese, and a common one is with たら. Genki states the following: "When we say 'A たら B', we mean that 'B is valid, contingent on the fulfillment of A.' That is to say, the event, action, or situation in B is realized if and when the condition A is met."

日本に行ったら、着物を買います。
I will buy a kimono if and when I go to Japan.

The た in たら comes from the plain past tense ending of words. The following list shows the plain form of the word, followed by the affirmative and negative たら conjugations.

Verbs:

• 読む
• 読んだら
• 読まなかったら

I-Adjectives:

• やさしい
• やさしかったら
• やさしくなかったら

Na-Adjectives:

• 静か
• 静かだったら
• 静かじゃなかったら

Nouns:

• 休み
• 休みだったら
• 休みじゃなかったら

The たら clause in the sentence describes a possible condition, which is then followed by a secondary clause that describes the resulting consequence. The possible condition can be something very likely, or it can be something rather unlikely.

天気がよかったら、散歩に行きます。
We'll go for a walk, if the weather is fine.

山下先生に会ったら、そのことを聞こうと思います。
I will ask about it, if I see Professor Yamashita.

宝くじに当たったら、アムネスティにお金を送ります。
I would send money to Amnesty International, if I should win the lottery.

The situation in the たら clause can sometimes be something very probable, and in that case, the sentence is more of a "when" scenario that describes a sequence of events.

今晩、うちに帰ったら、電話します。
I will call you when I get home tonight.

宿題が終わったら、遊びに行きましょう。
Let's go out and have some fun once we're done with the homework.

How you interpret the たら clause depends on the context of the situation. Looking at the second to last sentence - if it's likely that you'll get home tonight, then the sentence reads more like "when." However, if you're not sure whether you'll be home tonight, then the sentence reads more like "if."

Finally, the たら clause can describe a situation that is extremely unrealistic, or something that's hypothetical.

私が猫だったら、一日中寝ているでしょう。
If I were a cat, I would be asleep all day long.

お金があったら、車を買うんですけど。
If I had money, I would buy a car.