Thus in order to understand social life, we must go beyond the mere analysis of factual causes and effects, i.e. of motives, interests, and reactions caused by actions: we have to understand every event as playing a certain characteristic part within the whole. The event gains its significance from its influence upon the whole, and its significance is therefore in part determined by the whole.
But can there be a law of evolution? Can these be a scientific law in the sense intended by T.H. Huxley when he wrote : "... he must be a half-hearted philosopher who ... doubts that science will sooner or later ... become possessed of the law of evolution of organic forms - of the unvarying order of that great chain of modern causes and effects of which all organic forms, ancient and modern, are the links ..."?
I believe that the answer to this question must be "No", and that the search for the law of the "unvarying order" in evolution cannot possibly fall within the scope of scientific method, whether in biology or in sociology. My reasons are very simple. The evolution of life on earth, or of human society, is a unique historical process. Such a process, we may assume, proceeds in accordance with all kinds of causal laws, for example the laws of mechanics, of chemistry, of heredity and segregation, of natural selection, etc. Its description, however is not a law, but only a singular historical statement.
while we may base scientific predictions on laws, we cannot (as every cautious statistician knows) base them merely on the existence of trends. A trend (we may again take population growth as an example) which has persisted for hundreds or even thousands of years may change within a decade, or even more rapidly than that.
The poverty of historicism, we might say, is a poverty of imagination. The historicist continuously upbraids those who cannot imagine a change in their little worlds; yet it seems that the historicist is himself deficient in imagination, for he cannot imagine a change in the conditions of change.
What the "sociology of knowledge" overlooks is just the sociology of knowledge - the social or public character of science. It overlooks the fact that it is the public character of science and of its institutions which impose a mental discipline upon the individual scientist, and which preserves the objectivity of science and its tradition of critically discussing new ideas.