Page:Russell - An outline of philosophy.pdf/139
is supported by an elephant, and the elephant does not fall because it is supported by a tortoise. When his European interlocutor said "But how about the tortoise?" he replied that he was tired of metaphysics and wanted to change the subject. "Force", as an explanation, is no better than the elephant and the tortoise. It is an attempt to get at the "why" of natural processes, not only at the "how". What we observe, to a limited extent, is what happens, and we can arrive at laws according to which observable things happen, but we cannot arrive at a reason for the laws. If we invent a reason, it needs a reason in its turn, and so on. "Force" is a rationalising of natural processes, but a fruitless one since "force" would have to be rationalised also.
When it is said, as it often is, that "force" belongs to the world of experience, we must be careful to understand what can be meant. In the first place, it may be meant that calculations which employ the notion of force work out right in practice. This, broadly speaking, is admitted: no one would suggest that the engineer should alter his methods, or should give up working out stresses and strains. But that does not prove that there are stresses and strains. A medical man works his accounts in guineas, although there are none; he obtains a real payment, though he employs a fictitious coin. Similarly, the engineer is concerned with the question whether his bridge will stand: the fact of experience is that it stands (or does not stand), and the stresses and strains are only a way of explaining what sort of bridge will stand. They are as useful as guineas, but equally imaginary.
But when it is said that force is a fact of experience, there is something quite different that may be meant. It may be meant that we experience force when we experience such things as pressure or muscular exertion. We cannot discuss this contention adequately without going into the relation of physics to psychology, which is a topic we shall consider at length at a later stage. But we may say this much: if you press your finger-tip upon a hard object, you have an experience which you attribute to your finger-tip,