William Hamilton on classification

Found and purchased a sixth edition copy of Sir William Hamilton's Lectures on Metaphysics Vol II yesterday. Previously I had only come across him from John Stuart Mill's An Examination of Sir William Hamilton's Philosophy, and supposed that he was some kind of idealist. But I am interested in the 19thC philosophers because they, unlike most modern philosophers, treat classification seriously. For example, in addition to Mill's System of Logic, there's also William Jevon's The Principles of Science, with an extensive chapter on classification.

Why did this drop out of modern philosophy? I can't say for sure - in part it may have been due to the shift from the older syllogistic logic (which required a classification to commence inference) to modern set theory and formal symbolic logic. It may also be due to something else that is interesting me right now - relations. In classical logic, relata were terms that stood in a binary relation only. Locke asserted that these were in the understanding only, and Anglo philosophers seemed to accept this - relations are semantic, conceptual or logical.

But this isn't the case in science. Nobody thinks that the parent-child relationship is merely conceptual. And neither did Locke - he has a section on "natural relations", in the Essay (2.28.2) in which he names these very relations. However, our understanding of natural relations is in the mind, according to him. Here Locke and his successors part company with biology, at least. There is nothing conceptual about the birth of a foal from its dam.

So biology and philosophy became distant to each other, barely speaking, on the matter of classification. When philosophers discussed biological classification, it was in terms of the metaphysics of the empiricists or the ideals of yore. When biologists discussed the logic of classification, it was in terms of the same metaphysics and logic.

I might type some extracts of Hamilton as I travel through him. He calls classification the "elaborative faculty" (or rather it is part of that faculty), which involves Comparison, and which is "supposed in every, the simplest, act of knowledge ... our factitiously simple, our factitiously complex, and our generalised notions, are all so many products of Comparison; ... [and] Judgement ... [and] Reasoning [are] identical with Comparison." [Lect. XXXIV, p 279]

Hamilton, William, Henry Longueville Mansel, and John Veitch. 1874. Lectures on metaphysics and logic. Edinburgh: Blackwood.

Jevons, W. Stanley. 1877. The principles of science: a treatise on logic and scientific method.

Mill, John Stuart. 1865. An examination of Sir William Hamilton's philosophy and of the principal philosophical questions discussed in his writings. Boston: William V. Spencer.

Mill, John Stuart. 1867. A system of logic, ratiocinative and inductive : being a connected view of the principles of evidence and the methods of scientific investigation. New York: Harper & Brothers. 2nd ed. London: Macmillan. First edition 1847.