Blackwoods Edinburgh Magazine | Page 5

theorem respecting the logical value of the syllogism to its legitimate corollary, have been led to impute uselessness and frivolity to the syllogistic theory itself, on the ground of the petitio principii which they allege to be inherent in every syllogism. As I believe both these opinions to be fundamentally erroneous, I must request the attention of the reader to certain considerations, without which any just appreciation of the true character of the syllogism, and the functions it performs in philosophy, appears to me impossible; but which seem to me to have been overlooked or insufficiently adverted to, both by the defenders of the syllogistic theory, and by its assailants.
"It must be granted, that in every syllogism, considered as an argument to prove the conclusion, there is a petitio principii. When we say--
'All men are mortal. Socrates is a man; THEREFORE Socrates is mortal'--
it is unanswerably urged by the adversaries of the syllogistic theory, that the proposition, Socrates is mortal, is presupposed in the more general assumption, All men are mortal; that we cannot be assured of the mortality of all men, unless we were previously certain of the mortality of every individual man; that if it be still doubtful whether Socrates, or any other individual you choose to name, be mortal or not, the same degree of uncertainty must hang over the assertion, All men are mortal; that the general principle, instead of being given as evidence of the particular case, cannot itself be taken for true without exception, until every shadow of doubt which could affect any case comprised with it, is dispelled by evidence aliund��, and then what remains for the syllogism to prove? that, in short, no reasoning from generals to particulars can, as such, prove any thing; since from a general principle you cannot infer any particulars, but those which the principle itself assumes as foreknown.
"This doctrine is irrefragable; and if logicians, though unable to dispute it, have usually exhibited a strong disposition to explain it away, this was not because they could discover any flaw in the argument itself, but because the contrary opinion seemed to rest upon arguments equally indisputable. In the syllogism last referred to, for example, or in any of those which we previously constructed, is it not evident that the conclusion may, to the person to whom the syllogism is presented, be actually and bona fide a new truth? Is it not matter of daily experience that truth previously undreamt of, facts which have not been, and cannot be, directly observed, are arrived at by way of general reasoning? We believe that the Duke of Wellington is mortal. We do not know this by direct observation, since he is not yet dead. If we were asked how, this being the case, we know the Duke to be mortal, we should probably answer, because all men are so. Here, therefore, we arrive at the knowledge of a truth not (as yet) susceptible of observation, by a reasoning which admits of being exhibited in the following syllogism--
'All men are mortal. The Duke of Wellington is a man; THEREFORE The Duke of Wellington is mortal.'
"And since a large portion of our knowledge is thus acquired, logicians have persisted in representing the syllogism as a process of inference or proof; although none of them has cleared up the difficulty which arises from the inconsistency between that assertion and the principle, that if there be any thing in the conclusion which was not already asserted in the premisses, the argument is vicious. For it is impossible to attach any serious scientific value to such a mere salvo, as the distinction drawn between being involved by implication in the premisses, and being directly asserted in them. When Archbishop Whately, for example, says that the object of reasoning is 'merely to expand and unfold the assertions wrapt up, as it were, and implied in those with which we set out, and to bring a person to perceive and acknowledge the full force of that which he has admitted,' he does not, I think, meet the real difficulty requiring to be explained; namely, how it happens that a science like geometry can be all 'wrapt up' in a few definitions and axioms. Nor does this defence of the syllogism differ much from what its assailants urge against it as an accusation, when they charge it with being of no use except to those who seek to press the consequence of an admission into which a man has been entrapped, without having considered and understood its full force. When you admitted the major premiss, you asserted the conclusion, 'but,' says Archbishop Whately, 'you asserted it by implication merely; this, however, can here only mean that you asserted it unconsciously--that you did not know you were asserting it; but if