OBS. 35.—­Having now, as I imagine, clearly shown the difference between the restrictive and the resumptive sense of a relative pronoun, and the absolute necessity of making such a choice of words as will express that sense only which we intend; I hope the learner will see, by these observations, not merely that clearness requires the occasional use of each of our five relatives, who, which, what, that, and as; but that this distinction in the meaning, is a very common principle by which to determine what is, and what is not, good English.  Thus that and as are appropriately our restrictive relatives, though who and which are sometimes used restrictively; but, in a resumptive sense, who or which is required, and required even after those terms which usually demand that or as:  thus, “We are vexed at the unlucky chance, and go away dissatisfied. Such impressions, which ought not to be cherished, are a sufficient reason for excluding stories of that kind from the theatre.”—­Kames, El. of Crit., ii, 279.  Here which is proper to the sense intended; but such requires as, when the latter term limits the meaning of the former.  In sentences like the following, who or which may be used in lieu of that; whether with any advantage or not, the reader may judge:  “You seize the critical moment that is favorable to emotion.”—­Bair’s Rhet., p. 321. “An historian that would instruct us, must know when to be concise.”—­Ib., p. 359.  “Seneca has been censured for the affectation that appears in his style.”—­Ib., p. 367.  “Such as the prodigies that attended the death of Julius Caesar.”—­Ib., p. 401.  “By unfolding those principles that ought to govern the taste of every individual.”—­Kames’s Dedication to El. of Crit. “But I am sure he has that that is better than an estate.”—­Spect., No. 475.  “There are two properties, that characterize and essentially distinguish relative pronouns.”—­Churchill’s Gram., p. 74.  By these examples, it may be seen, that Dr. Blair often forgot or disregarded his own doctrine respecting the use of this relative; though he was oftener led, by the error of that doctrine, to substitute which for that improperly.

OBS. 36.—­Whether was formerly used as an interrogative pronoun, in which sense it always referred to one of two things; as, “Ye fools and blind! for whether is greater, the gold, or the temple that sanctifieth the gold?”—­Matt., xxiii, 17.  This usage is now obsolete; and, in stead of it, we say, “Which is greater?” But as a disjunctive conjunction, corresponding to or, the word whether is still in good repute; as, “Resolve whether you will go or not.”—­Webster’s Dict. In this sense of the term, some choose to call whether an adverb.