In formulating the laws of human thought, the logicians recognized what they called the fallacy of too few heads of classification. This might be called the fallacy of ignorance or of immaturity. It is characteristic of immature minds, the child mind and the beginnings of any science. To the child who has just learned the meaning of "papa" and "mamma," it often happens that all men are " papas" and all women are “mammas," while the child born in certain localities believes that all men are either white or black. Similarly in the beginnings of science, we are limited through a lack of knowledge to a few heads of classification and our development comes by increasing our genera or species. Coming more closely to our particular problem, we find that for many years, mankind has been divided into those who are sane and those who are insane, the latter class including all those people whose behavior was so far from established norms that they could not get along comfortably in the world by themselves.

To-day the mental defectives or feeble-minded are alluded to in England as cases of congenital insanity. However, of late, we have begun to draw a rather sharp line between insanity and mental

PROC. AMER. PHIL. SOC. LI. 205 I, PRINTED JULY 23, 1912.

defect or feeble-mindedness, the distinction being that feeblemindedness is an arrest of development whereas insanity is a degenerative process, the victim not simply stopping where he is but losing a part of the mentality that he once had. In the early years of childhood, it is practically impossible to differentiate between these two. The result is that we are apt to call everything feeblemindedness which occurs in the early years. And we have assigned as a cause of the feeble-mindedness whatever physical condition seems to be uppermost. For example, if we have a case of imbecility which also has hemiplegia, we classify it as a case of hemiplegic feeble-mindedness and assume, as a rule, that the cause which has resulted in the brain lesion producing the hemiplegia, has also caused the mental defect.

The thesis to be maintained in this paper is that this is not necessarily the case but rather that our whole problem will be simplified if we recognize some more heads of classification in this particular. To put the matter in another form, we may say that as the result of our study into the heredity of feeble-mindedness, we have come to the conclusion that the human family is divisible not only into the sane and insane, the healthy and diseased; but further, the sane and healthy group is subdivided possibly into many groups or strains; and that the mental capacity or possibilities varies widely in the different strains, but is fairly constant in each strain and is transmitted regularly, that is to say, so long as any given strain is kept pure, we will have the same mental capacity and possibilities generation after generation; that variations occur here as they do in the plant and lower animal world; that inbreeding and crossbreeding produce new combinations just as they do in plants or animals. To illustrate, we have only to call to mind almost any line of animal breeding. There is the genus horse, with various species, and within the species there are so-called strains. Every breeder knows that those strains will be transmitted and that they must be reckoned with in all attempts to breed horses for particular purposes or with particular characteristics. The same thing is true of dogs. No trainer would attempt to train a bull dog to retrieve or to point. Furthermore coming closer to our special problem, every trainer

knows that among the pointers, there are those that are easily and quickly trained to be high grade pointers; there are other strains that can never be trained to anything like the same efficiency.

The same thing seems to be true of the human race. There are strains that are capable of high mental development. These give us our geniuses or our brilliant leaders, or families with marked and valuable characteristics. Then there are strains with less capacity but still able to get along in the world and adapt themselves to their environment with fair success. These two groups are, of course, normal people. But when we go a step lower, we find a group of people whose capacity for development is so limited that they can never attain sufficient intelligence to get along in the world. Here we come to our group of feeble-minded and just as there are strains of varying degrees of intelligence which we call normal, so there are strains of varying degrees of defective intelligence, varying from those that are almost normal, almost able to take care of themselves, down to those who are so lacking in intelligence that they can do little more than procreate.

We are, for the time being, eliminating entirely all disease and abnormalities and fixing our attention upon what we call pure strains of feeble-mindedness. Furthermore, when this strain of pure feeble-mindedness is found uncomplicated as it often is, the mental condition is the chief peculiarity and the physical organism is oftentimes a remarkably perfect one, so that the strain is not recognized by any of its outward appearances, but only by those actions and movements which result from a less well-developed mentality. There can be found in institutions for the feeble-minded, persons of as fine physique and good health as can be found anywhere. This extends often even to details. For example: a dentist asserts that the finest set of teeth he has ever seen is in the mouth of an imbecile in an institution for feeble-minded.

Now it happens not unnaturally that these strains of defective mentality are liable to diseases of various kinds just as are socalled normal people. Whether the various diseases and accidents affect them in the same way as they affect people of normal intelligence, remains to be seen. It seems probable that in many cases the