THE LOGIC OF CLASSIFICATION. 235

"under it sub-class, cohort, order, &c. : and from the very circumstance that it stands thus high in other words, from the fact of its great generality it can only give us a very few attributes (five at most) characteristic of the whole mass of included particulars, and this not without striking ex- ceptions. But let us go a step or two lower down, let us take the ' Order' ; and what do we find ? We find that, by descending, we have reached a narrower grade ; and by this very fact of narrowing the grade in other words, of reducing the number of included members, we find we have increased the number of things we can predicate concerning these members, so that the characteristics that go to form the Order-mark are far more numerous than those that go to form the Class-mark. And so with the other grades as we descend : until at last we reach the Species (the unit of Classification, as the Individual is of Definition), where we have the minimum of extension with the maximum of mean- ing ; for the species, besides exhibiting the characteristics of the various grades above it, has numerous features peculiar to itself. In this way, we see at once the principle of the whole process. It is : The wider the group, the greater the number of included members, but the less the meaning conveyed respecting each member; and conversely. And the utility of the process consists in this : (1) that it throws intelligibility into a mass of materials that might otherwise remain unmanageable and incomprehensible, and is thereby an aid to knowledge ; (2) that it helps the memory, more especially in cases of enormous complication (such as we have in zoology and botany), where nothing would answer but a regular graded system of great perfection, group rising above group like the rounds of a stupendous ladder ; (3) that it facilitates the discovery and display of laws of coexistence. And this holds of all classification that is worthy of the name. We usually confine it to the Natural History group- ings : but it is equally true (though less conspicuously) of every grouping, of whatever materials, that is done upon a scientific basis from the classifications of things in ordinary life with a view to action, to the high abstract classifications of the sciences, where theory in great measure supersedes practice. This being so, it may not be amiss to inquire into the principles that govern scientific classification, and how far, under the most favourable circumstances, they can carry us. I. The first may be formulated thus : That our plan of