According to the wide definition of grammar, everyone uses some grammar, but nevertheless it's not a category error to say "*this sentence got grammar mistake".

When we speak about the grammar for a language/dialect we imply a prescribed "correct" grammar for a particular community of speakers.

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ninalanyon 2 hours ago | parent [-]

> speak about the grammar for a language/dialect we imply a prescribed "correct" grammar

Not prescribed, rather observed. At least in English where there is no language authority and dictionaries present usage.

The situation is even stranger in Norway where there is a prescribed form but where dialects have essentially equal rights so that the prescription really applies only to formal written Norwegian.

	▲	falcor84 an hour ago \| parent [-]
		From what I experienced, "proper" English grammar is absolutely prescribed at schools, and "poor grammar" will consistently and very predictably get you point deductions, regardless of whether linguists would accept your grammar as valid.