Page:Russell - An outline of philosophy.pdf/318
percept of our head. The failure to keep physical and perceptual space distinct has been a source of great confusion in philosophy.
In Part III. we resumed the study of man, but now as he appears to himself, not only as he is known to an external observer. We decided, contrary to the view of the behaviourists, that there are important facts which cannot be known except when the observer and observed are the same person. The datum in perception, we decided, is a private fact which can only be known directly to the percipient; it is a datum for physics and psychology equally, and must be regarded as both physical and mental. We decided later that there are inductive grounds, giving probability but not certainty, in favour of the view that perceptions are causally connected with events which the percipient does not experience, which may belong only to the physical world.
The behaviour of human beings is distinguished from that of inanimate matter by what are called "mnemic" phenomena, i.e. by a certain kind of effect of past occur rences. This kind of effect is exemplified in memory, in learning, in the intelligent use of words, and in every kind of knowledge. (But we cannot, on this ground, erect an absolute barrier between mind and matter. In the first place, inanimate matter, to some slight extent, shows analogous behaviour—e.g. if you unroll a roll of paper, it will roll itself up again. In the second place, we find that living bodies display mnemic phenomena to exactly the same extent to which minds display them. In the third place, if we are to avoid what I have called "mnemic" causation, which involves action at a distance in time, we must say that mnemic phenomena in mental events are due to the modification of the body by past events. That is to say, the set of events which constitutes one man's experi ence is not causally self-sufficient, but is dependent upon causal laws involving events which he cannot experience.
On the other hand, our knowledge of the physical world is purely abstract: we know certain logical characteristics