In the psychological way of defining a “mind”, it consists of all the mental events connected with a given mental event by “experience”, _i.e._ by mnemic causation, but this definition needs a little elaboration before it can be regarded as precise. We do not want the contraction of the pupil to count as a “mental” event; therefore a mental event will have to be one which has mnemic effects, not merely mnemic causes. In that case, however, there cannot be a last mental event in a man’s life, unless we assume that it may have mnemic effects on his body after death. Perhaps we may avoid this inconvenience by discovering the _kind_ of event that usually has mnemic effects, though they may be prevented from occurring by special circumstances. Or we might maintain that death is gradual, even when it is what is called instantaneous; in that case the last events in a man’s life grow progressively less mental as life ebbs. Neglecting this point, which is not very important, we shall define the “experience” to which a given mental event belongs as all those mental events which can be reached from the given event by a mnemic causal chain, which may go backwards or forwards, or alternately first one and then the other. This may be conceived on the analogy of an engine shunting at a junction or where there are many points: any line that can be reached, by however many shuntings, will count as part of the same experience. We cannot be sure that all the mental events connected with one body are connected by links of mnemic causation with each other, and therefore we cannot be sure that our two definitions of one “mind” give the same result. In cases of multiple personality, some at least of the usual mnemic effects, notably recollection, are absent in the life of one personality when they have occurred in the life of the other. But probably both personalities are connected by mnemic chains with events which occurred before the dissociation took place, so that there would be only one mind according to our definition. But there are other possibilities which must be considered. It may be that each cell in the body has its own mental life, and that only selections from these mental lives go to make up the life which we regard as ours. The “unconscious” might be the mental lives of subordinate parts of the body, having occasional mnemic effects which we can notice, but in the main separate from the life of which we are “conscious”. If so, the mental events connected with one body will be more numerous than the events making up its central “mind”. These, however, are only speculative possibilities.