eparation between the two
natures is now greatly mitigated. We can provide them with two systems
of relations in common; for both natures can be presumed to occupy the
same space and the same time. The theory now is this: Causal events
occupy certain periods of the absolute time and occupy certain positions
of the absolute space. These events influence a mind which thereupon
perceives certain apparent events which occupy certain periods in the
absolute time and occupy certain positions of the absolute space; and
the periods and positions occupied by the apparent events bear a
determinate relation to the periods and positions occupied by the causal
events.

Furthermore definite causal events produce for the mind definite
apparent events. Delusions are apparent events which appear in temporal
periods and spatial positions without the intervention of these causal
events which are proper for influencing of the mind to their perception.

The whole theory is perfectly logical. In these discussions we cannot
hope to drive an unsound theory to a logical contradiction. A reasoner,
apart from mere slips, only involves himself in a contradiction when he
is shying at a _reductio ad absurdum_. The substantial reason for
rejecting a philosophical theory is the 'absurdum' to which it reduces
us. In the case of the philosophy of natural science the 'absurdum' can
only be that our perceptual knowledge has not the character assigned to
it by the theory. If our opponent affirms that his knowledge has that
character, we can only--after making doubly sure that we understand
each other--agree to differ. Accordingly the first duty of an expositor
in stating a theory in which he disbelieves is to exhibit it as logical.
It is not there where his trouble lies.

Let me summarise the previously stated objections to this theory of
nature. In the first place it seeks for the cause of the knowledge of
the thing known instead of seeking for the character of the thing known:
secondly it assumes a knowledge of time in itself apart from events
related in time: thirdly it assumes a knowledge of space in itself apart
from events related in space. There are in addition to these objections
other flaws in the theory.

Some light is thrown on the artificial status of causal nature in this
theory by asking, why causal nature is presumed to occupy time and
space. This really raises the fundamental question as to what
characteristics causal nature should have