How to Say “Because” in Japanese | Using ～ので for Giving Polite Reasons

level1 (N5)

Introduction

You’ve probably already learned that から can be used to say “because” in Japanese. But did you know that there’s a softer, more polite way to say the same thing?

Meet 〜ので — another way to express “because,” often used in formal situations, explanations, and written language.

In this article, you’ll learn:

  • How to use ～ので with verbs, adjectives, and nouns
  • How it differs from 〜から
  • How to sound more natural and polite in Japanese conversation

1. Grammar Pattern

Short (Plain) form + ので

Meaning: “because / since / so”

To express “because” using ので, follow these steps:
1. Conjugate the verb, adjective, or noun in its short (plain) form (either present or past tense).
2. Add ので after the short form.

When using ので with な-adjectives & nouns in present tense, you have to add な before ので.

TypeExampleResult
Verb帰かえる帰るので (because I’m going home)
い-adjective忙いそがしい忙しいので (because I’m busy)
な-adjectiveしずかなしずかなので (because it’s quiet)
Noun学生がくせい学生なので (because [they] are a student)

2. Example Sentences

  • 頭あたまが痛いたいので、帰かえってもいいですか？
    = I have a headache, so may I go home?
  • わたしはベジタリアンなので、肉にくを食たべません。
    = Because I’m a vegetarian, I don’t eat meat.
  • 今日きょうは日曜日にちようびなので、銀行ぎんこうは休やすみです。
    = The bank is closed because today is Sunday.
  • 雨あめが降ふっているので、出でかけません。
    = Because it’s raining, I won’t go out.

3. How is ～ので Different from ～から?

While both ので and から express “because,” ので is generally considered more polite and formal.

  • から is used in spoken language, and is used when describing the reason/cause of something in a subjective way.
  • ので is used in both spoken and written language. It is used when describing the reason/cause in an objective way.

Example Comparison:

  • 時間じかんがないから、行いきません。
    = I’m not going because I don’t have time. (casual)
  • 時間がないので、行きません。
    = Since I don’t have time, I won’t go. (polite)

Context: Two middle schoolers talking about a new game.

A: Bought that game? – あのゲーム買かった？
B: Nah, no money so… – いや、お金かねがないから…

In this situation, if B said お金かねがないので (Okane ga nai node), it would sound unnaturally polite and weird for friends talking casually.

4. Conjugation Reminders

Typeので phrase
Verb (present)食たべる → 食べるので
Verb (past)行いった → 行ったので
い-adjectiveたのしい → たのしいので
な-adjectiveげんきな → げんきなので
Noun先生せんせい → 先生なので

💡 Don’t forget the な before ので with nouns & な-adjectives!

5. Practice Time!

Convert the following to 〜ので sentences:

EnglishJapanese
I’m tired, so I’ll sleep early.疲つかれているので、早はやく寝ねます。
It’s nice weather, so I’ll do laundry.いい天気てんきなので、洗濯せんたくします。
I caught a cold, so I stayed home.風邪かぜをひいたので、家いえで休やすみました。
I received a gift, so I’m happy.プレゼントをもらったので、うれしいです。
It’s Sunday, so I’m free.日曜日にちようびなので、ひまです。

6. FAQ – Frequently Asked Questions

Q
Can I start a sentence with ～ので?
A

Yes, and it’s common in formal contexts. Example: 雪ゆきが降ふっているので、 今日きょうは出でかけません。= Because it’s snowing, I won’t go out today.

Q
Can I use ～ので in casual conversation?
A

Yes, but it feels more polite. In very casual situations, ～から is more common.

Q
What if I forget the な for な-adjectives or nouns?
A

Your sentence may sound awkward or grammatically wrong.
Always say: しずかなので、がくせいなので

Q
Why do I need な before ので with な-adjectives and nouns (e.g., 学生なので)? Why not だ?
A

This is a specific rule for connecting present affirmative な-adjectives and nouns to ので (and also to んです/の). While the plain form ends in だ (e.g., 学生だ), this だ changes to な when followed directly by ので. Think of な as the required linking form in this specific grammatical context. For い-adjectives (e.g., 忙しい) and verbs (e.g., 行く), you use their standard plain forms directly before ので (忙しいので, 行くので).

Q
Since ので itself sounds polite, does the final sentence ending also need to be polite (ます/です)?
A

Generally, yes. Because ので carries a polite and somewhat formal nuance, it naturally pairs best with a polite sentence ending (using ます/です). While you might occasionally hear it followed by a plain form in certain contexts, it’s much more common and standard to maintain politeness: [Plain Form Reason] + ので + [Polite Main Clause]. Ex: 「時間がないので、失礼します。」 (Jikan ga nai node, shitsurei shimasu. – Since I don’t have time, please excuse me.)

7. Conclusion

Now you can express polite reasons using:

✅ Short-form verbs, adjectives, and nouns + ので
✅ Polite, formal-sounding “because”
✅ Proper use of な with nouns and な-adjectives

🎯 Try this: Write 3 polite sentences using 〜ので to explain why you’re doing (or not doing) something!

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