riyū wa ~ desu / ~ node / dōshite ~? / naze ~?… Expressions to explain “reason” in Japanese

When you express your opinion in Japanese, not only do you have to assert your position, but you also have to explain your reasons and evidence to convince your listeners. So how do you explain your reasons and evidence in Japanese? Here we will introduce a wide range of ways to explain “reasons,” from expressions that can be used in formal situations to those used in casual conversations between friends.

1.　理由は～です(riyū wa ~desu)

“理由は～です” (riyū wa ~desu) is one of the simple expressions used when explaining reasons. It is generally used in formal occasions such as school debates and business talks with customers. It is a polite expression ending with “～です” (desu), so it can be used in various situations regardless of the person you are talking to.

Example

僕は店舗の移転に反対します。理由は、店舗移転の費用が予算を上回っているからです。

Boku wa tenpo no iten ni hantai shimasu. Riyū wa, tenpo iten no hiyō ga yosan wo uwamawatte iru kara desu.

I disagree the relocation of the store. The reason is that the cost of relocating the store exceeds the budget.

You can also use “なぜなら～だからです” (nazenara ~dakara desu) in the same way as “理由は～です” (riyū wa ~desu) in the standard Japanese expression for explaining reasons.

Example

私は佐藤さんの提案に賛成です。なぜなら佐藤さんの提案は他の提案よりも費用対効果が高いからです。

Watashi wa Satō-san no teian ni sansei desu. Nazenara Satō-san no teian wa hoka no teian yori mo hiyōtaikōka ga takai kara desu.

I agree with Mr. Sato's proposal. Because Mr. Sato's proposal is more cost-effective than other proposals.

When using these expressions to explain reasons, be sure to express your position on the subject in the preceding statement.

2.　だって～だから(datte ~dakara)

“だって～だから” (datte ~dakara) is one of the casual Japanese expressions when you say reasons. “だって” (datte) means “because.” It is useful to use this expression when the person you are talking to asks why.

Example

A: どうして日本語を勉強しているの？

B: だって、日本が好きだから。

A: Dōshite Nihongo wo benkyō shiteiru no?

B: Datte, Nihon ga sukida kara.

A: Why do you study Japanese?

B: Because I like Japan.

The phrase “だって～だから” (datte ~dakara) is short, easy to remember, and convenient for explaining reasons, but if you use it when you are being warned or held accountable, it can be taken as an excuse. Be careful not to give the wrong impression.

Example

A: 昨日はどうして電話に出てくれなかったの？

B: だって、寝ていて電話に気づかなかったから。

A: Kinō wa dōshite denwa ni detekurenakatta no?

B: Datte, nete ite denwa ni kizukanakatta　kara.

A: Why didn’t you answer my call yesterday?

B: Because I was sleeping and didn't notice the call.

3.　～ので(~node)

The phrase “～ので” (node) is another expression that can be used to explain a reason. The word “～ので” (node) is a conjunction, which connects the previous sentence to the sentence after it to explain the reason. Therefore, the sentence before the “～ので” (node) explains the reason, while the sentence after “～ので” (node) explains the result.

Example

電車が遅延していたので、学校の授業に遅刻した。

Densha ga chien shite ita node, gakkō no jugyō ni chikoku shita.

The train was delayed, so I was late for my school class.

[日本のことが気になる？一緒に日本語を学びませんか？]

4.　～のため(~no tame)

“～のため” (~no tame) like “～ので” (node), is a conjunction used to explain the reason and convey the result. It gives a more polite impression to the other person. And so, this expression is often heard in formal situations such as train and bus announcements and workplace meetings.

Example

本日、この列車は強風のため速度を落として運行しています。

Honjitsu, kono ressha wa kyōfū no tame sokudo wo otoshite unkō shite imasu.

Today, this train is slowing down due to strong winds.

Example

外出中のため席を外しております。

Gaishutsu-chū no tame seki wo hazushite orimasu.

I’m not at my desk because I’m out.

Next, how about when you ask someone why they are doing something? Here are other examples.

5.　どうして～？(dōshite ~?)

Example

どうしてあなたは眠いのですか？

Dōshite anata wa nemui no desu ka?

Why are you sleepy?

6.　なぜ～？(naze ~?)

“どうして～？” (dōshite ~?) gives a little childish impression, so basically if you use this “なぜ～？” (naze ~?), there should be no problem. So if you're having trouble remembering “どうして～？” (dōshite ~?), just remember “なぜ～？” (naze ~?).

Example

なぜ早起きをしなくてはならなかったの？

Naze hayaoki wo shinakute wa naranakatta no?

Why did you have to get up early?

Example

なぜあなたはトレーニングをしているの？

Naze anata wa torēningu wo shite iru no?

Why are you training?

7.　なんで～？(nande ~?)

Use “なんで～？” (nande ~?) for friends and younger people. Be careful that it may be rude to ask your superiors “なんで～？” (nande ~?) in Japan.

Example

なんで仕事を休んだの？

Nande shigoto wo yasunda no?

Why were you absent from work?

There are various expressions when asking or explaining the reason. If you are interested in the Japanese language, why don't you sign up for a free membership to Human Academy Japanese Language School Plus. You can experience practical Japanese lessons by experienced teachers for free.