It is only in cases susceptible of a rule, that any writer can be judged deficient.

I can censure no man for differing from me, till I can show him a principle which he ought to follow.

According to Lord Kames, the standard of taste, both in arts and in manners, is "the common sense of mankind," a principle founded in the universal conviction of a common nature in our species.

(See _Elements of Criticism_, Chap, xxv, Vol.

ii, p.
364.) If this is so, the doctrine applies to grammar as fully as to any thing about which criticism may concern itself.
But, to the discerning student or teacher, I owe an apology for the abundant condescension with which I have noticed in this volume the works of unskillful grammarians.