500 G. E. T. BOSS: wholly nearer to the sun than it. But our exclusive major premiss in virtue of which we drew our conclusion was founded on the fact that outside and inside are specific differ- entiations of spatial relations, that nothing which is out is in. The exclusive force of our disjunction is then indirectly a priori and built upon the logical principle of individuation, and is of no particular interest to the science of astronomy ; the real force of the disjunction lies in its exhaustiveness, the denial that there are any planets with orbits intersecting that of the earth. Contrast the statement " Planets whose orbits lie between the earth and the sun are, when visible, to be seen either in the morning or in the evening ". Now there is no general self-evident principle which states that a heavenly body visible in the morning is not, during the same period, visible in the evening. The incompatibility of these two predicates has to be deduced from the nature of the particular subject treated of planets between the earth and the sun. But we may very well make and employ the above disjunction without possessing this proof, without knowing that Venus, when visible in the evenings, must rise after the sun and be lost in his light in the morning. Hence we see that the force of the disjunction lies in its exhaustiveness, while the exclusiveness, if present, depends upon the predicates in- volved in each case. A classification is of value chiefly for its exhaustiveness. It is a predication of the properties of a genus taken concretely. As such it is an ideal of science and like the predication of property, that with which science may rest content. But for the practical life it is the starting-point of activity ; it is the possession of this kind of knowledge which the practical life desires. We wish to know the whole number of types into which a genus is divided, so that we may have confidence when to expect to find the qualities common to the whole class. For example, we wish to know the complete tale of the ores of iron so that in our prospecting we may know what substances to collect and test if we are in- vestigating the possibilities of iron mining in a certain district. It is not sufficient to know that the particular ore (B) is iron-producing (A) and that C, D and E fall under the same category. What we wish to be sure of is that the list is exhaustive, that all not-B is C D or E, and all not-C is D, E or B. The specific difference of each of the various sorts of minerals may be taken for granted, but to assert it is not the purpose of a judgment of this kind. Again, if we cannot identify a certain species with any of the members
