Of the many views that have been put forward on this question two or three call for some attention. In the opinion of Thomists generally, the principle which individuates _material_ things, thus multiplying numerically the same specific nature, is to be conceived as a positive mode affecting the latter and revealing it in a new aspect, whereas the specific nature of the _spiritual_ individual is itself formally an individual. The principle of the latter’s individuation is already involved in the very concept of its specific nature, and therefore is not to be conceived as a distinct positive aspect of the latter but simply as the absence of plurality and communicability in the latter. In material things, moreover, the positive mode or aspect whereby the specific nature is found numerically multiplied, and incommunicable as it exists in each, consists in the fact that such a specific nature involves in its very constitution a _material_ principle which is actually allied with certain _quantitative dimensions_. Hence the principle which individuates material substances is not to be conceived—after the manner in which Scotists conceive it—as an ultimate _differentia_ affecting the _formal_ factor of the nature, determining the specific nature just as the _differentia specifica_ determines the generic nature, but as a _material_ differentiating principle. What individuates the material individual, what marks it off as one in itself, distinct or divided from other individuals of the same specific nature, and incommunicable in that condition, is the material factor of that individual’s nature—not, indeed, the material factor, _materia prima_, considered in the abstract, but the material factor as proximately capable of actual existence by being allied to certain more or less definite spatial or quantitative dimensions: “matter affected with quantity”: “_materia quantitate signata_”.(146) In regard to material substances this doctrine embraces two separate contentions: (_a_) that the principle which individuates such a substance must be conceived as something positive, not really distinct from, but yet not contained in, the specific nature considered in the abstract; (_b_) that this positive aspect is to be found not in the formal but in the material principle of the composite corporeal substance.