History of Western Philosophy - Bertrand Russell [374]
I do not propose, at present, to decide between these four points of view. The decision, if possible at all, can only be made by an elaborate investigation of non-demonstrative inference and the theory of probability. What I do propose to do is to point out certain logical errors which have been committed by those who have discussed these questions.
Berkeley, as we have seen, thinks that there are logical reasons proving that only minds and mental events can exist. This view, on other grounds, is also held by Hegel and his followers. I believe this to be a complete mistake. Such a statement as 'there was a time before life existed on this planet', whether true or false, cannot be condemned on grounds of logic, any more than 'there are multiplication sums which no one will have ever worked out'. To be observed, or to be a percept, is merely to have effects of certain kinds, and there is no logical reason why all events should have effects of these kinds.
There is, however, another kind of argument, which, while it does not establish idealism as a metaphysic, does, if valid, establish it as a practical policy. It is said that a proposition which is unverifiable has no meaning; that verification depends upon percepts; and that, therefore, a proposition about anything except actual or possible percepts is meaningless. I think that this view, strictly interpreted, would confine us to the first of the above four theories, and would forbid us to speak about anything that we have not ourselves explicitly noticed. If so, it is a view that no one can hold in practice, which is a defect in a theory that is advocated on practical grounds. The whole question of verification, and its connection with knowledge, is difficult and complex; I will, therefore, leave it on one side for the present.
The fourth of the above theories, which admits events that no one perceives, may also be defended by invalid arguments. It may be held that causality is known a priori, and that causal laws are impossible unless there are unperceived events. As against this, it may be urged that causality is not a priori, and that whatever regularity can be observed must be in relation to percepts. Whatever there is reason to believe in the laws of physics must, it would seem, be capable of being stated in terms of percepts. The statement may be odd and complicated; it may lack the characteristic of continuity which, until lately, was expected of a physical law. But it can hardly be impossible.
I conclude that there is no a priori objection to any one of our four theories. It is possible, however, to say that all truth is pragmatic, and that there is no pragmatic difference between the four theories. If this is true, we can adopt whichever we please, and the difference between them is only linguistic. I cannot accept this view; but this, also, is a matter for discussion at a later stage.
It remains to be asked whether any meaning can be attached to the words 'mind' and 'matter'. Everyone knows that 'mind' is what an idealist thinks there is nothing else but, and 'matter' is what a materialist thinks the same about. The reader knows also, I hope, that idealists are virtuous and materialists are wicked. But perhaps there may be more than this to be said.
My own definition of 'matter' may seem unsatisfactory; I should define it as what satisfies the equations of physics. There may be nothing satisfying