example of the general law that, in mnemic causation, the causal
unit is not one event at one time, but two or more events at two or more
times.& A burnt child fears the fire, that is to say, the neighbourhood
of fire has a different effect upon a child which has had the sensations
of burning than upon one which has not. More correctly, the observed
effect, when a child which has been burnt is put near a fire, has for
its cause, not merely the neighbourhood of the fire, but this together
with the previous burning. The general formula, when an animal has
acquired experience through some event A, is that, when B occurs at some
future time, the animal to which A has happened acts differently from
an animal which A has not happened. Thus A and B together, not either
separately, must be regarded as the cause of the animal's behaviour,
unless we take account of the effect which A has had in altering the
animal's nervous tissue, which is a matter not patent to external
observation except under very special circumstances. With this
possibility, we are brought back to causal laws, and to the suggestion
that many things which seem essentially mental are really neural.
Perhaps it is the nerves that acquire experience rather than the mind.
If so, the possibility of acquiring experience cannot be used to define
mind.*

* Cf. Lecture IV.

Very similar considerations apply to memory, if taken as the essence of
mind. A recollection is aroused by something which is happening now,
but is different from the effect which the present occurrence would
have produced if the recollected event had not occurred. This may be
accounted for by the physical effect of the past event on the brain,
making it a different instrument from that which would have resulted
from a different experience. The causal peculiarities of memory may,
therefore, have a physiological explanation. With every special class of
mental phenomena this possibility meets us afresh. If psychology is
to be a separate science at all, we must seek a wider ground for its
separateness than any that we have been considering hitherto.

We have found that "consciousness" is too narrow to characterize mental
phenomena, and that mnemic causation is too wide. I come now to a
characteristic which, though difficult to define, comes much nearer to
what we require, namely subjectivity.

Subjectivity, as a characteristic of mental phenomena, was considered in
Lecture VII, in connection w