Original nature thus sets the scope and the limits of an individual's character and achievement. It tells "how much" and, in the most general way, "what" his capacities are. Thus a man born with a normal vocal apparatus can speak; a man born with normal vision can see. But what language he shall speak, and what sights he shall see, depend on the social and geographical situation in which he happens to be placed. Again, if a man is born with a "high general intelligence," that is, with keen sensory discriminations and motor responses, precise and accurate powers of analysis of judgment, a capacity for the quick and effective acquisition and modification of habits, we can safely predict that he will excel in some direction. But whether he will stand out as a lawyer, doctor, philosopher, poet, or executive, it is almost impossible from original nature to tell.[1] [Footnote 1: The psychological tests used in the army, and being used now with modifications in the admission of students to Columbia College, are "general intelligence" tests. That is, they show general alertness and intellectual promise, but are not prophetic of any specialized talents or capacities.] INDIVIDUAL DIFFERENCES--DEMOCRACY AND EDUCATION. The fact that individuals differ in ability and interest has important consequences for education and social progress. It means, in the first place, that while current optimistic doctrines about the modifiability of human nature are true, they are true within limits--limits that vary with the individual. Whether or not we shall ever succeed, through the science or the practice of eugenics, in eliminating low ability and perpetuating high exclusively, the fact remains that there are in contemporary society the widest variations both in the kinds of interest and ability displayed, and in their relative efficacy under present social and industrial conditions. There are, it must be noted at the outset, a not inconsiderable number of individuals who must be set down as absolute social liabilities. Even if existing social and educational arrangements were perfect, these would remain unaffected and unavailable for any useful purpose. They would have to be endowed, cared for, or confined. There is the quite considerable class, who, while normal with respect to sensory and motor discrimination, seem to be seriously and irremediably defective in their powers of judgment. These also seem to offer invulnerable resistance to education, and their original natures would not be subject to modification even by an education perfectly adapted to the needs of normal people.