essential and accidental properties, between what it must always exhibit and what it might dispense with.

A person who had lived all his life on the shore of the Atlantic, would believe, unless otherwise informed, that every other sea resembled this in all particulars, in its tidal movement, though the Mediterranean is almost tideless, in its degree of saltness, though the taste of the Dead Sea is much more bitter and its composition different, and so on. In travelling, or in reading a book of travels, he is made acquainted with another sea with properties not quite identical indeed, but still so far similar that he cannot help regarding the new specimen as of the same kind as the old. This he sees at once upon making the comparison of the two objects; and he then proceeds to reflect upon the properties of each, with a view to discover the points in which they agree, as well as those in which they are at variance. Having ascertained what they are, he sees that a separation must be made between the dispensable and the indispensable properties, because the latter will belong to each and every specimen of this kind, whilst the former, as he now sees, need not be present to constitute a sea what it is. He proceeds then to abstract, or draw off (abstrahere), the points in which seas are to agree from those in which they may differ; and the properties so drawn off and kept apart, are called the Notes or Marks or Attributes of a sea, and form when taken together a

Universal or Common Nature (Universale). But he cannot think of a common nature without implying a class of things, be the number large or small, in each of which this set of attributes is to be found, and each of which must exhibit them as its credentials for admission into the class; in taking this further step he generalises, or forms a Genus or Class. Lastly, as he cannot be sure of remembering the class, nor hope to recall it to the minds of others who have gone through, or who at least take for granted, the same steps of thought, without a name to represent it, he either invents a new name, or applies that by which he once designated a single thing, to the whole class; which is an act of Denomination.

There are here no less than five steps, which must have been taken by every one who fully and fairly realises a general notion, and some of which must have been made even by those who have a less distinct apprehension of what they mean when they speak of classes. i. Comparison is the act of putting together two or more single objects with a view to ascertain how far they resemble each other. ii. Reflection is ascertainment of their points of resemblance and their points of difference. iii. Abstraction is the separation of the points of agreement from those of difference, that they may constitute a new nature, different from, yet including, the single objects. iv. Generalisation is the recognition of a class of things,

each of which is found to possess the abstracted marks. v. Denomination is the imposition of a name that shall serve to recall equally the Genus or Class, and the Common Nature.

The process thus analysed into five acts is often described generally by the principal of them, as Abstraction; and for convenience' sake that word shall be reckoned sufficient here.

§ 49. Higher and Lower Conceptions.

The functions of Abstraction do not cease, as soon as we have compared several intuitions, to form one conception. We may proceed to form a larger conception from several narrower ones; and this too is done by Abstraction. By observing John, Thomas, and Peter, and abstracting from their accidents the essential marks, we get the notion of man; but again, by comparing the conception man with other conceptions, cow, sheep, wolf, whale, and observing the mark common to all, that they suckle their young, we form the wider conception Mammalia, -wider, because it concludes man and many other conceptions. We may carry the process farther still; and, with writers on Natural History, compare the Mammalia, with Aves, Amphibia, Pisces, Insectæ, and Vermes, when we shall discover that all these, however different, agree in having life and sensation, from which

marks we gain the new conception animal, wider than any of the former, as including them all,-higher, as requiring a second step in the abstractive process to reach it.

§ 50. Genus, Species, Individual.

In this scale, composed of more or fewer steps, the lowest is always the intuition or Individual. The next is called the Lowest Species (infima species), which can only contain single objects, not subordinate kinds or classes. All the higher rounds of the ladder, except the highest, are called Subaltern (subalterna) Genera, which are alternately genera and species, genera to the lower, and species to the higher and wider conceptions. The widest class, with which Abstraction ceases, is called the Highest (summum) Genus, because in this hierarchy of conceptions it is not brought under any other genus as its species, but is itself the genus to each conception in the series. Thus the

Individual is neither genus nor species.

Infima Species is never a genus.

Summum Genus is never a species.

Subalterna Genera are genera to those below them, and species to those above.*

With the Greek Logicians the Summum Genus is yévos γενικώτατον, the Infma Species, εἶδος εἰδικώτατον, the subaltern genus, εἶδος μέσον καὶ ὑπάλληλον.

A series of this kind, in which the same individuals are found throughout, is called a system of cognate genera. Thus, in the series Socrates, Philosopher, Man, Animal, the same individual, Socrates, is found in each of the three conceptions, and might have the name of it applied to him.

It must be remarked that the Summum Genus and the Infima Species are fixed somewhat arbitrarily. There can only be one absolute summum genus, and we may go on abstracting until we come to some wide notion, be it "thing" or "substance " or "essence or "object," that comprehends all that we can think about. If we stop short of this, as the Naturalist does when he makes Animal his highest genus, the name can only be used in a qualified sense, and our genus is only the highest because we will make it so. Then, we can scarcely ever ascertain the infima species, or that kind that is too narrow to be divided into other kinds, because even in a handful of individuals we cannot say with certainty that there are no distinctions upon which a further subdivision into classes might be founded.

The genus next above a given species is called proximate; those that are still higher are called remote. A number of species that have the same proximate genus are said to be co-ordinate.

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