y our knowledge is brought
before us when we realise our thoughts in any discussion of the causes
of our perceptions. For example, the fire is burning and we see a red
coal. This is explained in science by radiant energy from the coal
entering our eyes. But in seeking for such an explanation we are not
asking what are the sort of occurrences which are fitted to cause a mind
to see red. The chain of causation is entirely different. The mind is
cut out altogether. The real question is, When red is found in nature,
what else is found there also? Namely we are asking for an analysis of
the accompaniments in nature of the discovery of red in nature. In a
subsequent lecture I shall expand this line of thought. I simply draw
attention to it here in order to point out that the wave-theory of light
has not been adopted because waves are just the sort of things which
ought to make a mind perceive colours. This is no part of the evidence
which has ever been adduced for the wave-theory, yet on the causal
theory of perception, it is really the only relevant part. In other
words, science is not discussing the causes of knowledge, but the
coherence of knowledge. The understanding which is sought by science is
an understanding of relations within nature.

So far I have discussed the bifurcation of nature in connexion with the
theories of absolute time and of absolute space. My reason has been that
the introduction of the relational theories only weakens the case for
bifurcation, and I wished to discuss this case on its strongest grounds.

For instance, suppose we adopt the relational theory of space. Then the
space in which apparent nature is set is the expression of certain
relations between the apparent objects. It is a set of apparent
relations between apparent relata. Apparent nature is the dream, and
the apparent relations of space are dream relations, and the space is
the dream space. Similarly the space in which causal nature is set is
the expression of certain relations between the causal objects. It is
the expression of certain facts about the causal activity which is going
on behind the scenes. Accordingly causal space belongs to a different
order of reality to apparent space. Hence there is no pointwise
connexion between the two and it is meaningless to say that the
molecules of the grass are in any place which has a determinate spatial
relation to the place occupied by the grass which we see. This
conclusion is very parado