The Historical Evidence claims our attention in the first instance; but in no question of literary genuineness is this the sort of proof which yields the surest grounds of conviction. [Sidenote: I. External Evidence.] Such questions arise only under circumstances in which the external proof on either side is very weak, and the internal evidence has therefore to be continually resorted to for supplying the defects of the external. It is true that a complete proof of a work having been actually written by a particular person, destroys any contrary presumption from intrinsic marks; and, in like manner, when a train of evidence is deduced, showing it to be impossible that a work could have been written by a certain author, no internal likeness to other works of his can in the least weaken the negative conclusion. [Sidenote: Historical evidence cannot exclude internal, unless the former is complete.] In either case, however, the historical evidence must be incontrovertible, before it can exclude examination of the internal; and the two cases are by no means equally frequent. It scarcely ever happens that there is external evidence weighty enough to establish certainly, of itself, an individual's authorship of a particular work; but the external proof that his authorship was impossible, may often be convincing and perfect, from an examination of dates, or the like. Since, therefore, external evidence against authorship admits of completeness, we are entitled, when such evidence exclusively is founded on, to demand that it shall be complete. Where by the very narrowest step it falls short of a demonstration of absolute impossibility, the internal evidence cannot be refused admittance in contravention of it, and comes in with far greater force than that of the other. There may be cases where authorship can be made out to the highest degree, at least, of probability, by strong internal evidence coming in aid of an external proof equally balanced for and against; and even where the extrinsic proof is of itself sufficient [3:1]to infer improbability, internal marks may be so decided the opposite way, as to render the question absolutely doubtful, or to occasion a leaning towards the affirmative side. [Sidenote: Internal evidence the true test for _The Two N. K._] These principles point out the internal evidence as the true ground on which my cause must be contested; but it was not necessary to follow them out to their full extent; for I can show you, that the external facts which we have here, few as they are, raise a presumption in favour of Shakspeare's authorship, as strong as exists in cases of more practical importance, where its effect has never been questioned. [Sidenote: _The Two N. K._ printed in 1634 as by Fletcher and Shakspere.]