The province of English grammar is, rightly considered, wider than is indicated by any one of the above definitions; and the student ought to have a clear idea of the ground to be covered.
Few inflections.
It must be admitted that the language has very few inflections at present, as compared with Latin or Greek; so that a small grammar will hold them all.
Making rules is risky.
It is also evident, to those who have studied the language historically, that it is very hazardous to make rules in grammar: what is at present regarded as correct may not be so twenty years from now, even if our rules are founded on the keenest scrutiny of the "standard" writers of our time. Usage is varied as our way of thinking changes. In Chaucer's time two or three negatives were used to strengthen a negation; as, "Ther nas no man nowher so vertuous" (There never was no man nowhere so virtuous). And Shakespeare used good English when he said more elder ("Merchant of Venice") and most unkindest ("Julius Cæsar"); but this is bad English now.
If, however, we have tabulated the inflections of the language, and stated what syntax is the most used in certain troublesome places, there is still much for the grammarian to do.
A broader view.
Surely our noble language, with its enormous vocabulary, its peculiar and abundant idioms, its numerous periphrastic forms to express every possible shade of meaning, is worthy of serious study, apart from the mere memorizing of inflections and formulation of rules.
Mental training. An æsthetic benefit.
Grammar is eminently a means of mental training; and while it will train the student in subtle and acute reasoning, it will at the same time, if rightly presented, lay the foundation of a keen observation and a correct literary taste. The continued contact with the highest thoughts of the best minds will create a thirst for the "well of English undefiled."