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."
Every one 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 these equations; in that case either physics
or the concept "matter" is a mistake. If we reject substance, "matter" will have to be a logical
construction. Whether it can be any construction composed of events--which may be partly
inferred--is a difficult question, but by no means an insoluble one.
As for "mind," when substance has been rejected a mind must be some group or structure of
events. The grouping, must be effected by some relation which is characteristic of the sort of
phenomena we wish to call "mental." We may take memory as typical. We might-though this
would be rather unduly simple-define a "mental" event as one which remembers or is
remembered. Then the "mind" to which a given mental event belongs is the group of events
connected with the given event by memory-chains, backwards or forwards.