Page:Mind (Old Series) Volume 12.djvu/448

 ON THE DOCTRINE OF NATURAL KINDS, 435 that in many treatises of logic the earlier is not noticed. Lastly, four of the Predicables have been a third time appropriated, and are used by biologists in a technical sense. By means of Likeness (an ultimate element) Things are to be thought of "in those groups respecting which a greater number of general assertions can be made, and those assertions more important than could be made respecting any other groups into which the same things could be distributed " (Mill). After all this arranging of Things by means of intensive attri- butes mentally abstracted from the things (for subject and attri- bute are in reality one, as Prof. Bain and Mill emphatically show) after all this, we are told that there are in nature Divisions of Kind, bounded by impassable barriers. At first sight this seems an unlooked-for harmony of the actual with the theoretical. Here are Classes ready formed for us. But let us listen to their definition and criteria, and perplexities thicken. Mill says that a Kind is one of those classes which are distin- guished from all others, not by one or a few definite properties, but by an unknown multitude of them ; the combination of pro- perties on which the class is grounded being a mere index to an indefinite number of other distinctive attributes, and instances Plant, Animal, Sulphur, Horse, &c., as Kinds. Sometimes the properties on which we ground a class exhaust all that it has in common, or contain it all by some mode of implication. In other instances a selection is made of a few properties from a number inexhaustible by us. Where a certain apparent difference between things (though perhaps in itself of little moment) answers to we know not what number of other differences pervading not only their known properties, but properties yat undiscovered, it is not optional but imperative to recognise this difference as the founda- tion of a specific distinction. He tells us that there are in nature distinctions of Kind, that they are parted off from one another by an unfathomable chasm instead of a mere ordinary ditch, and that our knowledge of the properties of a kind is never complete. See Logic, bk. i. c. 7 ; iii. 22, 25 ; iv. 6, 7. OBJ. 1. It is plain, from the above doctrine, that we cannot form our Classes that are Kinds on the basis of attributes, as logic has heretofore directed us to do. We cannot tell what many of the attributes are, nor are we to expect to do so. Yet we have made the group. But how ? By connecting the things through some few attributes they have in common, and then, desisting from working by intension, grouping them, as it were, in exten- sion, and postulating that they must have unknown common attributes. Is this procedure reconcilable with Mill's own analysis of the classificatory process ? OBJ. 2. Two criteria are given for determining whether a made class is a Kind. First, that a Kind shall have an unknown multi- tude of properties, not merely derivable from one another, the combination of properties on which the class is grounded being a