3. Man, a compound of body (matter) and of soul (form), puts forth activities of a higher order—knowledge and volition. Through his senses he perceives concrete objects, e.g. this oak; through his intellect he knows the abstract and universal (the oak). All our intellectual activity rests on sensory function; but through the active intellect (intellectus agens) an abstract representation of the sensible object is provided for the intellectual possibility. Hence the characteristic of the idea, its non-materiality, and on this is based the principal argument for the spirituality and immortality of the soul. Here, too, is the foundation of logic and of the theory of knowledge, the justification of our judgments and syllogisms.