If this be so, and so it most assuredly is--if the proper functions of the Understanding be that of generalizing the notices received from the senses in order to the construction of _names_: of referring particular notices (that is, impressions or sensations) to their proper names; and, _vice versâ_, names to their correspondent class or kind of notices--then it follows of necessity, that the Understanding is truly and accurately defined in the words of Leighton and Kant, a "faculty judging according to sense."
Now whether in defining the speculative Reason (that is, the Reason considered abstractedly as an _intellective_ power) we call it "the source of necessary and universal principles, according to which the notices of the senses are either affirmed or denied;" or describe it as "the power by which we are enabled to draw from particular and contingent appearances universal and necessary conclusions:"[97] it is equally evident that the two definitions differ in their essential characters, and consequently the subjects differ in _kind_.
The dependence of the Understanding on the representations of the senses, and its consequent posteriority thereto, as contrasted with the independence and antecedency of Reason, are strikingly exemplified in the Ptolemaic System (that truly wonderful product and highest boast of the faculty, judging according to the senses!) compared with the Newtonian, as the offspring of a yet higher power, arranging, correcting, and annulling the representations of the senses according to its own inherent laws and constitutive ideas.
[94] See Wisd. of Sol. vii. 22, 23, 27.--H. N. C.
[95] Accordingly as we attend more or less to the differences, the _sort_ becomes, of course, more or less comprehensive. Hence there arises for the systematic naturalist, the necessity of subdividing the sorts into orders, classes, families, &c.: all which, however, resolve themselves for the mere logician into the conception of _genus_ and _species_, _i.e._ the comprehending and the comprehended.
[96] Were it not so, how could the first comparison have been possible?--It would involve the absurdity of measuring a thing by itself. But if we think on some one thing, the length of our own foot, or of our hand and arm from the elbow joint, it is evident that in _order_ to do this, we must have the conception of measure. Now these antecedent and most general conceptions are what is meant by the constituent _forms_ of the Understanding: we call them _constituent_ because they are not _acquired_ by the Understanding, but are implied in its constitution. As rationally might a circle be said to acquire a centre and circumference, as the Understanding to acquire these, its inherent _forms_, or ways of conceiving. This is what Leibnitz meant, when to the old adage of the Peripatetics, _Nihil in intellectu quod non prius in sensu_ (There is nothing in the Understanding not derived from the Senses, or--There is nothing _con_ceived that was not previously _per_ceived;) he replied--_præter intellectum ipsum_ (except the Understanding itself).