such and so

such before (adjective +) noun

We use such before a noun (with or without an adjective).

• They’re such fools. (not They’re so fools.)
• It was such good milk that we couldn’t stop drinking it. (not It was so good milk that …)

Such comes before a/an.

• She’s such a baby.
• I’ve never met such a nice person. (not … a such/so nice person.)

so before adjective, adverb, etc

We use so before an adjective alone (without a noun) or an adverb.

• She’s so babyish. (not She’s such babyish.)
• The milk was so good that we couldn’t stop drinking it.
• Why do you talk so slowly?

We can also use so before much, many, few and little.

• We’ve got so much to do, and so little time.

We use so much, not so, before comparatives.

• I’m glad you’re feeling so much better. (not … so better.)

note

For so beautiful a day, etc, (see here).

For more about the meaning and use of such, (see here). For more about so, (see here).