The fundamental proposition of the apriorist theory is that knowledge is made up of two sorts of elements, which cannot be reduced into one another, and which are like two distinct layers superimposed one upon the other.[16] Our hypothesis keeps this principle intact. In fact, that knowledge which is called empirical, the only knowledge of which the theorists of empiricism have made use in constructing the reason, is that which is brought into our minds by the direct action of objects. It is composed of individual states which are completely explained[17] by the psychical nature of the individual. If, on the other hand, the categories are, as we believe they are, essentially collective representations, before all else, they should show the mental states of the group; they should depend upon the way in which this is founded and organized, upon its morphology, upon its religious, moral and economic institutions, etc. So between these two sorts of representations there is all the difference which exists between the individual and the social, and one can no more derive the second from the first than he can deduce society from the individual, the whole from the part, the complex from the simple.[18] Society is a reality _sui generis_; it has its own peculiar characteristics, which are not found elsewhere and which are not met with again in the same form in all the rest of the universe. The representations which express it have a wholly different contents from purely individual ones and we may rest assured in advance that the first add something to the second. Even the manner in which the two are formed results in differentiating them. Collective representations are the result of an immense co-operation, which stretches out not only into space but into time as well; to make them, a multitude of minds have associated, united and combined their ideas and sentiments; for them, long generations have accumulated their experience and their knowledge. A special intellectual activity is therefore concentrated in them which is infinitely richer and complexer than that of the individual. From that one can understand how the reason has been able to go beyond the limits of empirical knowledge. It does not owe this to any vague mysterious virtue but simply to the fact that according to the well-known formula, man is double. There are two beings in him: an individual being which has its foundation in the organism and the circle of whose activities is therefore strictly limited, and a social being which represents the highest reality in the intellectual and moral order that we can know by observation--I mean society. This duality of our nature has as its consequence in the practical order, the irreducibility of a moral ideal to a utilitarian motive, and in the order of thought, the irreducibility of reason to individual experience. In so far as he belongs to society, the individual transcends himself, both when he thinks and when he acts.