"Because I had a headache, I didn't go to work." In Japanese, you can say this with から or ので. But they're not freely interchangeable — the difference is subtle, yet it's a common exam topic.
Basic Structure
| Conjunction | How it connects | Example |
|---|---|---|
| から | Polite or plain form | 暇ですから、散歩しましょう。 |
| ので | Must use plain form before it | 暇なので、散歩しましょう。 |
When using ので after nouns and na-adjectives, だ changes to な:
❌ 暇だので
✅ 暇なので
Core Difference: What Gets Emphasized
This is the fundamental distinction between から and ので:
| から | ので | |
|---|---|---|
| Emphasizes | The reason (before) | The result (after) |
| Tone | Subjective, direct | Objective, softer |
Japanese people tend to prefer ので. The reason is simple — using から feels like you're saying "it's because of THIS, it's not my fault," while ので softly puts the focus on the result, which sounds more polite.
Compare:
頭痛がしたから、行きませんでした。 → It's because I had a headache, so I didn't go. (emphasizing "I had a headache")
頭痛がしたので、行きませんでした。 → I had a headache, so I didn't go. (emphasizing "didn't go")
The ので Restriction
ので has one hard rule — it cannot be followed by these sentence types:
| Can't follow ので | Reason |
|---|---|
| Requests (〜てください) | Subjective demand |
| Commands (〜なさい) | Subjective order |
| Invitations (〜ませんか) | Subjective proposal |
| Speculation (〜でしょう) | Subjective judgment |
These all express the speaker's will, which clashes with ので's objective, mild character.
Concrete example:
✅ 暇ですから、一緒に公園を散歩しませんか？ → Since I'm free, shall we take a walk in the park? (から + invitation = OK)
❌ 暇なので、一緒に公園を散歩しませんか？ → ので followed by invitation ませんか = unnatural
When making requests, commands, or invitations, always use から.
から's Freedom
Compared to ので's restrictions, から is much more flexible:
- The clause before it can be polite or plain form
- Any sentence type can follow it — no restrictions
In modern Japanese, whether you use plain or polite form before から makes little difference:
頭痛がしたから、行きませんでした。 (plain + から)
頭痛がしましたから、行きませんでした。 (polite + から)
Both are perfectly fine.
Comparison Summary
| Feature | から | ので |
|---|---|---|
| Emphasizes | Reason | Result |
| Tone | Subjective, direct | Objective, softer |
| What comes before | Plain or polite form | Plain form (nouns/na-adj: だ→な) |
| What comes after | No restrictions | No requests, commands, invitations, or speculation |
| Japanese preference | General situations | More polite situations |
Bonus: なぜなら — State the Result First, Explain Later
Japanese also has the conjunction なぜなら, which works the opposite way — state the result first, then explain the reason, ending with から:
今日は人が多い。なぜなら、今日はバーゲンだから。 → There are a lot of people today. Why? Because there's a sale today.
The structure is: A. なぜなら、B + から.
Summary
- から emphasizes the reason, has no restrictions on what follows
- ので emphasizes the result, is more polite, but can't be followed by requests, commands, or invitations
- Before ので, use plain form; nouns/na-adjectives change だ to な
- Japanese people tend to prefer ので for its softer tone
- When using ませんか / てください, you must choose から
Practice Questions
1. Fill in the blank: 病気＿＿＿、学校を休みました。(Use ので)
Show answer
病気なので、学校を休みました。
Explanation: 病気 is a noun, so だ changes to な before ので.
2. Is this sentence natural? 「暇なので、一緒に映画を見ませんか？」
Show answer
It's unnatural. ので cannot be followed by the invitation pattern ませんか. It should be:
暇ですから、一緒に映画を見ませんか？
3. What does から emphasize and what does ので emphasize?
Show answer
- から emphasizes the reason before it (subjective, direct)
- ので emphasizes the result after it (objective, softer)