<Logic>.We may now look at his work on Logic, which is a very elaborate one, and contains very able discussions and learned notes.It proceeds upon a very thorough acquaintance with Aristotle and his commentators, with the schoolmen and the logical writers of the seventeenth century; but was directly suggested by the Kantian criticism and amendment of logic, and by the works of such men as Esser, Fries, Krug, and Drobisch, who carried out the principles of the great German metaphysician.just as the " Port Royal Logic " has all the excellencies and defects of the philosophy of Descartes, so the logic of Hamilton has the combined truth and error of the metaphysics of Kant.It should be added, that his analytic; so far drawn from German sources in some of its fundamental views, is, after all, Hamilton's own, in the way in which it is wrought out and applied.Logic is defined as "the science of the laws of thought as thought."It is represented to be an <a priori> science."It considers the laws of thought proper as contained <a priori> in the nature of pure intelligence." He does not state, and evidently does not see, that these laws of thought, while not the laws of the objects of thought, {449} are laws of thought as employed about objects, and can be discovered not <a priori>, but simply by an observation of the workings of thought.
He reviewed the not very philosophical but very shrewd and useful work of Whately, in the " Edinburgh Review " for 1833, criticising it with terrible severity, and giving indications of his own views.He was already cogitating his system, he expounded it to his class after he became professor, and he gave it to the public in "An Essay toward a new Analytic of Logical Forms," being that which gained the prize proposed by Sir William Hamilton, in the year 1846, for the best exposition of the new doctrine propounded in his lectures, with an historical appendix, by Thomas Spencer Baynes.It would require a treatise as elaborate as Hamilton's two volumes to state and examine it in detail, but I may notice some of the fundamental points.
<The Concept>.It proceeds on the distinction between the extension and comprehension of a term or notion.He makes no pretensions to the discovery of this principle.He knew that it was stated in the "Port Royal Logic," and that it was taught in Glasgow University by Hutcheson.Professor Baynes has shown in his translation of the "Port Royal Logic" that there were anticipations of it in earlier works.
Hamilton carries out the distinction more thoroughly than it had ever been before." The comprehension of a concept is nothing more than the sum or complement of the distinguishing characters or attributes of which the concept is made up; and the extension of a concept is nothing more than the sum or complement of the objects themselves, whose resembling characters were abstracted to constitute the concept." (Vol.I., P.148.) If we except his exposition of this distinction, he does not seem to me to throw much light, otherwise, on the first part of logic, -- the part as it appears to me which has most need to be cleared up.He draws no distinction between the general notion and the abstract notion, but treats of both under the one designation, concept.But surely there is a distinction between two such notions as "animal" on the one band, embracing an indefinite number of objects, and " life,"which has not a complement of objects, but is only an attribute of objects.{450}
<Judgment>.He claims originality chiefly for his doctrine of the thorough quantification of the predicate.
"Touching the principle of an explicitly quantified predicate, I bad by 1833 become convinced of the necessity to extend and correct the logical doctrine on this point." "Before 1840 I had become convinced that it was necessary to extend the principle equally to negatives." (Vol."., P.
209.) This doctrine, as Professor Baynes shows, had been partially anticipated, but had never been fully carried out.
I am inclined to admit that the credit, if there be any credit, in the thorough quantification of the predicate belongs to Hamilton.But I set no value on the supposed improvement.It proceeds on the simple logical postulate, "to state explicitly what is thought implicitly." I admit the principle, but deny that it requires the predicate to be universally quantified.When we say "the dog barks," we make the predication, without inquiring in thought whether there are or are not other dogs that bark, whether dogs are all or only some barking animals.When we say " man is rational,"we do not determine whether or no there are other creatures that are rational; whether, for example, angels may be called rational, whether men are "all" or only "some"rational.As the predicate is not always or even commonly quantified in spontaneous thought, so we do not require always to quantify it in the logical enunciation.At the same time, it is of importance to be able to quantify it on demand, and thus to see reflectively what is involved in every proposition.In carrying out his principles, he adds to the four classes of propositions acknowledged in the received logic A, E, I, 0, other four, U.Common salt is chloride of sodium.
Y.Some stars are all the planets.
n.No birds are some animals.
w.Some common salt is not some chloride of sodium.