Page:Theory of Mind of Roger Bacon.djvu/11

 With Species so described, the importance of this theory for his Philosophy of Mind becomes apparent at once. And, indeed, Bacon directly calls attention to the vital importance of his treatise, on the Propagation of Species, for the understanding of his theory of Perception; the latter cannot be understood at all without the former. And conversely the action of the mind upon the body is explained by use of the same theory. In fact, all phenomena of qualitative change in the one world (spiritualia) as in the other (corporalia), and in their interaction, are to be brought within the scope of this single, far-reaching hypothesis. There is apparently no realm left untouched by the “laws of the propagation of Species, which the sense of sight follows in common with all other senses, and with the whole machine of the universe.” And as one turns the pages whereon lie registered the hopes and expectations of our Author for this theory of his, he knows not which to admire the more, the genius that could give meaning to his thought, or the courage that could face its full execution. Certain it is, in any case, that it forms “the warp and the woof” for his Philosophy of Mind.

It has already been indicated, that Bacon’s theory of Species is an attempt to explain change of a certain kind; not change in position, nor change in quantity, but change in quality. This