“It is by their emphasis on schemes of thought that the Greeks founded the various branches of science, which have remade civilization. A proposition which falls within a scientific scheme is accepted with surprisingly slight direct verification. For example, at the present time we all accept the famous doctrine of the shift of the spectral lines. But so far as direct evidence is concerned, there are some experiments on rays from the sun, with very dubious interpretations, and the clear-cut instance of the light from the dark companion of Sirius. There are millions of untested stars, apart from the question as to whether the same star will always give the same effect. But no one doubts the doctrine because it falls within the reigning scientific scheme. The importance of the scheme is illustrated by imagining some occurrence which does not fall within any scheme. You go to a strange foreign country, and among your first observations on your first day is that of a man standing on his head. If you are cautious, you will refrain from generalizing on the propensity of the inhabitants to stand on their heads; also half your friends will disbelieve you when you mention the incident. Yet your direct evidence is comparable to that respecting the shift of the spectral lines.
“The production of a scheme is a major effort of the speculative Reason. It involves imagination far outrunning the direct observations. The interwoven group of categoreal notions which constitute the scheme allow of derivative extension by the constructive power of deductive logic. Throughout the whole range of these propositions respecting the interrelations of the forms of things, some of them allow of direct comparison with experience. In this way, the scheme as a whole has contact with experience. The extent of its conformity or non-conformity with observed fact can thus be explored. A scheme which, for a time at least, is useless methodologically, is one which fails to yield these observable contacts with fact.
“An abstract scheme which is merely developed by the abstract methodology of logic, and which fails to achieve contact with fact by means of a correlate practical methodology of experiment, may yet be of the utmost importance. The history of modern civilization shows that such schemes fulfil the promise of the dream of Solomon. They first amplify life by satisfying the peculiar claim of the speculative Reason, which is understanding for its own sake. Secondly, they represent the capital of ideas which each age holds in trust for its successors. The ultimate moral claim that civilization lays upon its possessors is that they transmit, and add to, this reserve of potential development by which it has profited. One main law which underlies modern progress is that, except for the rarest accidents of chance, thought precedes observation. It may not decide the details, but it suggests the type. Nobody would count, whose mind was vacant of the idea of number. Nobody directs attention when there is nothing that he expects to see. The novel observation which comes by chance is a rare accident, and is usually wasted. For if there be no scheme to fit it into, its significance is lost. The way of thoughtless nature is by waste — a million seeds, and one tree; a million eggs, and one fish. In the same way, from a million observations of fact beyond the routine of human life it rarely happens that one useful development issues.” (From Whitehead’s The Function of Reason)