Between two clauses I had always been taught throughout primary school that two independent clauses within one sentence must be separated by a comma; however I see many writing or typing sentences such as, "He came early, but she came late." as, "He came early but she came late." Is this some new rule or is there more incorrect omission of commas nowadays? Given that I am not entirely old, as I started attending primary school in the early 1990s, I remember that omission of a comma in such cases was absolutely incorrect and was castigated via the lowering of marks of the assignment for each comma omitted, amongst other grammatical errors (e.g. subtraction of one mark per omitted comma).