The danger is, however, that, being preoccupied with describing and explaining and having used abstractions so successfully for these purposes, we may come to lose our sense of fact altogether and fail to distinguish between actual facts and the symbols which we use to explain them. This, indeed, is just what Bergson thinks really does happen. No doubt an intelligent physicist is perfectly aware that the vibrations and wave lengths and electrons and forces by which he explains the changes that take place in the material world are fictions, and does not confuse them with the actual facts in which his actual knowledge of the material world consists. But it is much more doubtful whether he distinguishes between these actual facts and the common sense material objects, such as lumps of lead, pieces of wood, and so on, which he probably believes he knows directly but which are really only abstractions derived from the facts in order to explain them just as much as his own vibrations and wave lengths. When a scientist frames a hypothesis he employs the intellectual method of substitution with full consciousness of what he is about; he recognises that its terms are abstractions and not facts. But the intellectual method of explaining by substituting general abstractions for particular facts is not confined to science. All description and explanation, from the first uncritical assumptions of common sense right up to the latest scientific hypothesis employs the intellectual method of substituting abstractions for actual facts. The common sense world of things, events, qualities, minds, feelings, and so on, in which we all pass our every day lives is an early and somewhat crude attempt to describe the continually changing fact which each of us experiences directly, but it is perhaps more misleading than the later elaborate constructions of chemistry, physics, biology or physchology in that things and qualities are more easily mistaken for facts than more obviously hypothetical assumptions. Bergson points out that the various things of which this common sense world consists, solid tables, green grass, anger, hope, etc., are not facts: these things, he insists, are only abstractions. They are convenient for enabling us to describe and explain the actual facts which each of us experiences directly, and they are based upon these facts in the sense of being abstracted from them. The objection to them is that we are too much inclined to take it for granted that these things and qualities and events actually are facts themselves, and in so doing to lose sight of the real facts altogether. In support of his view that things having qualities in successive relations are mere abstractions Bergson points out that whenever we stop to examine what it actually is that we know directly we can see at once that this fact does not consist of things and qualities at all: things and qualities are clearly marked off one from another,; they change as a