～ので

ので after a sentence gives a reason: "because", "so". The reason comes first, then ので, then what follows from it. A verb or い-adjective takes ので directly; a noun or な-adjective takes な in between.

Where から takes だ, ので takes な.

• × 学生だので → 学生なので
• × 静かだので → 静かなので

ので or から

Both give a reason. ので sounds softer and more polite, so it is the usual choice for apologies, excuses and explanations to someone above you, and before a polite request. から is more direct, and sits easily before a suggestion or an order. Only から can end a sentence with です.

• × 遅刻したのは電車が遅れたのでです → 遅刻したのは電車が遅れたからです

Usage notes

These go beyond the plain-form reason.

Polite form before ので

In very polite speech, at work or in announcements, the reason itself can be in the polite form: ですので, ますので.

Stopping at ので

A sentence can end on ので and leave the request or refusal unsaid. It is a soft way to excuse yourself.