The general law of association, or, more accurately, the common condition under which all exciting causes act, and in which they may be generalized, according to Aristotle is this. Ideas by having been together acquire a power of recalling each other; or every partial representation awakes the total representation of which it had been a part. In the practical determination of this common principle to particular recollections, he admits five agents or occasioning causes: first, connection in time, whether simultaneous, preceding, or successive; second, vicinity or connection in space; third, interdependence or necessary connection, as cause and effect; fourth, likeness; and fifth, contrast. As an additional solution of the occasional seeming chasms in the continuity of reproduction he proves, that movements or ideas possessing one or the other of these five characters had passed through the mind as intermediate links, sufficiently clear to recall other parts of the same total impressions with which they had co-existed, though not vivid enough to excite that degree of attention which is requisite for distinct recollection, or as we may aptly express it, after consciousness. In association then consists the whole mechanism of the reproduction of impressions, in the Aristotelian Psychology. It is the universal law of the passive fancy and mechanical memory; that which supplies to all other faculties their objects, to all thought the elements of its materials. In consulting the excellent commentary of St. Thomas Aquinas on the Parva Naturalia of Aristotle, I was struck at once with its close resemblance to Hume’s Essay on Association. The main thoughts were the same in both, the order of the thoughts was the same, and even the illustrations differed only by Hume’s occasional substitution of more modern examples. I mentioned the circumstance to several of my literary acquaintances, who admitted the closeness of the resemblance, and that it seemed too great to be explained by mere coincidence; but they thought it improbable that Hume should have held the pages of the Angelic Doctor worth turning over. But some time after Mr. Payne showed Sir James Mackintosh some odd volumes of St. Thomas Aquinas, partly perhaps from having heard that he had in his Lectures passed a high encomium on this canonized philosopher; but chiefly from the fact, that the volumes had belonged to Mr. Hume, and had here and there marginal marks and notes of reference in his own hand writing. Among these volumes was that which contains the Parva Naturalia, in the old Latin version, swathed and swaddled in the commentary afore mentioned