236 THE AMERICAN JOURNAL OF SOCIOLOGY
under the same conditions, and will change in the same way under like changes in the conditions.
As an abstract proposition all force is one, but there are a great many fields of phenomena due to as many different general conditions under which the universal force acts. It has been the custom to speak of the action of force under such dif- ferent conditions as the action of so many different forces. This is at least convenient, and so long as the law of the correlation of forces is recognized it can lead to no error.
Now, it follows from this that every true science must be a domain of force ; that each science must preside over some one of these various forces, and that any field of knowledge which has not been brought under the operation of some natural force is not yet a science in the proper sense of that word. The mere accumulation of facts does not constitute a science, but a success- ful classification of the facts recognizes the law underlying them and is, in so far, scientific. In fact, classification is always the initial step in the establishment of a science, and the more recon- dite workings of the force over which it presides are discovered later. We have only to look over the history of the several recognized sciences to see ample illustrations of these principles, and I cannot now stop to undertake an enumeration of them.
If, therefore, sociology is a science, it must agree with all others in this respect, and all knowledge that is not systematized according to this principle must be ruled out of the science of society. I have always maintained that sociology does con- stitute a science, capable of being submitted to this test, and if I have contributed anything to that science it has been in the direction of pointing out the nature of the social forces and the mode of their activity. I propose briefly to recapitulate the general results which I claim to have reached in this field of research.
In the first place the social forces are psychic. They have their seat in the mental constitution of the individual compo- nents of society. But here it is necessary to understand what the mind includes. The popular conception of mind is far too nar-
