p Sensory knowledge and abstract thought represent a unity: they reflect one and the same material world and have a common basis: the practical activity of mankind. Both these stages of knowledge have one physiological basis, man’s nervous system.

p Abstract thought is impossible without sensory knowledge inasmuch as the information furnished by the sense organs is the sole material for forming concepts. There can be nothing in thought that is not given to man by his sense organs. But, having arisen on the basis of sensations, abstract thought goes deeper than sensory knowledge, enriches and extends its bounds. Sensory impressions, illumined by the light of reason, acquire new content.

p Since the sensory and the logical act in unity, supplementing and enriching each other, neither the indications of the sensations nor the conclusions of reason must be ignored in the process of cognition. Yet there are trends in philosophy which understand the process of knowledge onesidedly.

p Supporters of empiricism (from the Greek empeiria, meaning experience) underestimate the role of abstract thought in knowledge, maintaining that sense impressions alone give man a true picture of the world. Since concepts cannot be perceived by the senses (it is impossible, for example, to imagine a “man in general”, a “tree in general”, and so on), empiricists claim that in reality nothing corresponds to concepts, that they are the product of man’s imagination.

p Empiricism is widespread in modern bourgeois philosophy and sociology. This is not surprising. Bourgeois ideologists fear broad generalisations and are anxious to avoid solutions of concrete social problems and withdraw into the realm of insignificant facts and superficial observations.

p In contrast to empiricists, supporters of rationalism do not trust the sense organs and consider reason, abstract thought the sole source of true knowledge. Rationalists underestimate the role of sensory knowledge and assume that man is capable of cognising the world intuitively, without any experience. By divorcing concepts and other forms of thought from sensations and perceptions, rationalists 162 ultimately lapse into idealism.

It follows that logical knowledge must not be divorced from sensory knowledge because this inevitably leads to a distortion of the cognitive process, to the divorce of thought from reality; this is typical of all trends of idealism. Idealism has certain gnosiological  [162•*  and class roots which account for its tenacity. Let us examine these roots.