JOSEPH PETZOLDT, I'll iloxop/ti,' ,li-r lu-nu'ii l<]rf<ili,'ti>ui. :(!>'.) unapt to show how Unity of Interest or Endeavour can furnish a synthetic principle of determination for the psychical process whereby that interest develops or that endeavour realises itself is undeniable. But just in so far as we can detect unity and continuity iu the mental life as we can do in all attentive processes provided we do not use these fundamental ideas too abstractly to that extent we have in hand a principle that can really explain mental development, explain, that is, how the development takes place, what determines it in one direction rather than in another, why mental change is a growth and not a flux. To discuss this fundamental point would lead us too far. We need only refer to Prof. Stout's truly psychological chapters on mental process and on association in his lately-published tfanual of Psychology. Admirers of Prof. Stout's work will probably find on reading Mr. Petzoldt's volume that the two central points on which they will fundamentally disagree with the latter are : (1) Its abstract conception of the data of psychology, which is such as to make a reconstruction of the psychical life out of its own analysed material quite impossible. (2) Its adoption of the hypothetical biological vital series as a working principle of psychological synthesis in the place of the clearly conceived but woefully neglected non-hypothetical psychical vital series. This latter as Prof. Stout's own treatment clearly shows, provides an admirable working principle for the explana- tion of mental development, and does not commit the student to any ultimate views as to the Unity of Consciousness. The first indictment may seem to be unjust. Avenarius doesn't spin webs out of his own brain except in Biology. His work bristles and reeks with facts. He is also very careful not to treat the individual as though he had no environment to reckon with. He is abstract only in this that he insists on having all his materials pure. But pure experience turns out to be experience purified of its vitality, the facts of consciousness, for instance, abstracted from the interest or endeavour that just makes them the facts of an individual self. The purified psychical processes are left like fishes in filtered water, or what is still worse, like fishes on dry land, finding their support outside their natural ele- ment. But what Science surely requires is simply experience purified of its confusions. Now when we are dealing with some- thing that is the product of growth this demand for a pure ex- perience does not simply mean the demand for a thoroughgoing analysis. The analysis must be throughout the differentiation of a principle, must, in fact, not only take the genetic form, but must be the analysis of a Self or an interest or of something that has in it the capacity to develop. It is of course quite possible to work out a purely analytic psychology on genetic lines. And this is indeed what Avenarius usually does, as witness his excellent analysis of conation. But the result of such an analysis is not