An Essay on Material Necessity !

At the one extreme stands Hume, who at least according to common conceptions rules out entirely the possibility of material or non-logical necessity, and who therefore rules out also the possibility that we might enjoy that sort of certain knowledge that earlier philosophers had assumed as a matter of course to be correlated therewith.' At the other extreme stands Adolf Reinach, the hero of our present story, who defends the existence of a wide class of material necessities falling within the domain of what can be a priori known. More precisely, Reinach holds that there are certain categories of entity whose factual instantiation brings with it as a matter of necessity the instantiation of certain other correlated categories. The instantia tion of the ca tegory color necessi ta tes in this fashion the instantiation of the category visual extension. Such categories are to be