I am a native speaker of English but am having trouble with the distinction between that and which, with respect to restrictive and non-restrictive clauses and comma usage.
For example, which is correct:
Dragons, that breath fire, are scary.
or
Dragons that breath fire are scary.
or
Dragons, which breath fire, are scary.
Since all dragons breath fire, breath fire seems to be descriptive or non-restrictive, so there should be no commas used.
My punctuation has never been that spot-on, although I don't have much trouble with other areas of grammar and syntax. I feel that punctuation heavily affects the readability of my writing even if the word-ordering of the sentence is grammatically correct. The links I've found about this have still left me slightly confused.
Cheers!
Edit: Upon some further reading, it seems that and which are technically interchangeable; however, that usually proceeds a restrictive clause, and which usually proceeds a non-restrictive clause. Please correct me if I'm wrong about this.
Reference: