atmosphere. But I am not sure that most persons would not be inclined to maintain that the mind is in the body 'somehow'—and when we inquire into the significance of this 'somehow,' we can scarcely fail to discover that it has a material flavor. Whether rightly or wrongly, most men think of the mind as in the body in somewhat—but only somewhat—the same way as material atoms may be in the body. And he who thinks of the mind in this way may, if the question occur to him at all, assume that mind and body interact somewhat as two material things interact with each other.
To be sure, the more one reflects upon the difference between mental phenomena and physical, the more vague and indefinite this 'somewhat' seems to become. Material things can lie beside one another in space; they can approach one another and recede from one another. Their interaction is a thing to be described in physical terms; we have to do with space and motions in space. Have we anything analogous to this when we are considering, let us say, the mental image of a railway station and those physical changes in the brain which antecede my moving my feet in the direction of the station? Is the mental image literally in any part of the brain? Can it approach or recede from any group of molecules? Does it mean anything to say that it lies between this physical occurrence and that? And if the relation between what is mental and what is physical is really so different from the relation between two physical things, must we not recognize that the word 'interaction' is ambiguous when it is applied indiscriminately to either relation?
As early as the seventeenth century reflection upon the differences which distinguished the mental and the physical led to the conclusion that it is impossible that ideas should be inserted as links in any physical chain of events. You can not plant an imaginary tree in a real ten-acre lot; you can not insert the thought of a cork into the neck of a real bottle; is it more sensible to say that the thought of a railway station may be inserted as a link in a series of changes in the nervous system of a man? To such men as Huxley and Clifford it seemed that the physical series must be regarded as unbroken. Clifford, much influenced by the philosopher Spinoza, describes the relation between physical changes in the brain and the accompanying ideas as a 'parallelism,' as a correspondence or concomitance. It is scarcely necessary to add that neither he nor any later parallelist has intended the word 'parallelism' to be taken literally. It only means that mental phenomena are to be regarded as excluded from the series of physical changes, and yet as accompanying them.
Now, I think we may leave out of consideration those who endeavor to steer a middle course—to eat their cake and, at the same time, to keep it. The question is: Is the series of physical changes to be re-
