Punctuation would be part of orthography which is usually considered distinct. Consider you can have multiple writing systems for a single language, that singl

Punctuation would be part of orthography which is usually considered distinct. Consider you can have multiple writing systems for a single language, that single language would have a single set of grammar rules, but would have multiple orthographic rules applied to it. Put another way, if I was to invent apostropheless English which was exactly like English but just omits all written apostrophes that wouldn't change the rules of English grammar, possessives would still be possessive etc.