The mistake into which the Titmice have been innocently led, however, is precisely that of dividing the practice which they would uphold, from the theory to which they would object. They should have been told in infancy, and thus prevented from exposing themselves in old age, that theory and practice are in so much _one_, that the former implies or includes the latter. A theory is only good as such, in proportion to its reducibility to practice. If the practice fail, it is because the theory is imperfect. To say what they are in the daily habit of saying—that such or such a matter may be good in theory but is false in practice,—is to perpetrate a bull—to commit a paradox—to state a contradiction in terms—in plain words, to tell a lie _which is a lie at sight_ to the understanding of anything bigger than a Titmouse. But we have no idea, just now, of persecuting the Tittlebats by too close a scrutiny into their little opinions. It is not our purpose, for example, to press them with so grave a weapon as the _argumentum ad absurdum_, or to ask them why, if the popularity of a book be in fact the measure of its worth, we should not be at once in condition to admit the inferiority of “Newton’s Principia” to “Hoyle’s Games;” of “Ernest Maltravers” to “Jack-the-Giant-Killer,” or “Jack Sheppard,” or “Jack Brag;” and of “Dick’s Christian Philosopher” to “Charlotte Temple,” or the “Memoirs of de Grammont,” or to one or two dozen other works which must be nameless. Our present design is but to speak, at some length, of a book which in so much concerns the Titmice, that it affords them the very kind of demonstration which they chiefly affect—_practical_ demonstration—of the fallacy of one of their favorite dogmas; we mean the dogma that no work of fiction can fully suit, at the same time, the critical and the popular taste; in fact, that the disregarding or contravening of Critical Rule is absolutely essential to success, beyond a certain and very limited extent, with the public at large. And if, in the course of our random observations—for we have no space for systematic review—it should appear, incidentally, that the vast popularity of “Barnaby Rudge” must be regarded less as the measure of its value, than as the legitimate and inevitable result of certain well-understood critical propositions reduced by genius into practice, there will appear nothing more than what has before become apparent in the “Vicar of Wakefield” of Goldsmith, or in the “Robinson Crusoe” of De Foe—nothing more, in fact, than what is a truism to all but the Titmice.