INTELLIGENCE or UNDERSTANDING is a term that is still used by psychologists with considerable latitude of meaning. Sometimes it is used as a synonym of "cognition," that is to say, it is applied to any of the numerous processes by which knowledge is built up. Sometimes it is restricted to the conceptual processes, as distinct from processes of sense perception. And sometimes it is used in the still more restricted sense of the process or function of apprehending relations, or even special kinds of relation. In view of the extensive use of so-called "intelligence tests" (q.v.) for all sorts of practical purposes, it would seem to be a matter of some urgency to determine as precisely as possible what is meant by intelligence. But that is not the view of many of the investigators in this branch of applied psychology. Some of them frankly admit that they do not know and do not care what this "intelligence" may be which they are measuring, so long as these measurements can be made use of. Others regard it as denoting the average mental ability of an individual in so far as this can be determined by a series of sample tests. Yet others identify it with some "general" ability which the individual possesses, besides certain "special" or "specific" abilities (see ABILITIES), and correlate the former with the general stock of "mental energy," and the latter with various "engines," into which this mental energy may be directed alternatively—whatever these physical metaphors may mean. Others again identify intelligence with the apprehension of rela tions of all kinds, or only with the function of apprehending connections. Lastly, ordinary everyday usage perhaps tends, on the whole, to emphasize the practical character of intelligence as consisting in the ability to employ the right means in order to achieve the various ends pursued.
The view put forward by the present writer is that the terms "intelligence" and "understanding" should be restricted to the mental function of apprehending connections. Such a conception, it is here maintained, is not only most in accord with ordinary usage, but also helps to explain most of the other uses of these terms. In order to make these points clear, it is necessary, first of all, to explain what is meant by connections. This term is used in the sense of causal and rational (or logical) relations, or relations of causal and rational (or logical) interdependence. All connections are relations, but not all relations are connections. Such simple relationships between things as, e.g., their similarity or difference are not connections, although they may afford some sort of evidence concerning their connections. Similarly, relations in space and in time are not connections, though these likewise may furnish evidence concerning their connections. The apprehension of these simpler relations seems to call for no other mental functions than those required for ordinary sense-percep tion. The same processes which render possible, say, the per ception of two patches of colour, also render possible our apprehension of their similarity or difference, of their local contiguity or distance, and of their simultaneity or succession. On the other hand, connections cannot as a rule be perceived, but must be conceived. That will explain why most psychologists restrict "intelligence" and "understanding" to conceptual proc esses. An example or two of our use of these terms will help to elucidate the view here maintained, and will also show its agree ment with ordinary usage. By looking at the several parts of a puzzle, or of a lock, one can see their similarities and differences, and their spatial relations, also certain time relations it may be. Everybody with normal sight can perceive that much. But not everybody can grasp, or grasp equally quickly or thoroughly, the connections between the various parts of the lock or the puzzle. And ordinary usage would associate the term "intelli gence" or "understanding" with an insight into these connections, not with the mere perception of the parts as separate items, or even with the perceptions of relations of similarity or difference, of space and time. Similarly, one would not say that anyone understands a proposition in geometry when he has merely learned it by heart, or has just ascertained by measurement that certain properties co-exist in a geometrical figure of a certain kind, but does not apprehend the connection between them. Nor again would anybody be said to understand an historical period or a geographical area if he had merely committed to memory a string of facts without any insight into the causes which produced them. This conception of intelligence will explain also the common association of the term with the practical application of the right means to achieve one's ends. For it is only when one has an idea of the connections between things, that one knows what methods will produce what results. Similarly with "learning from experience," which is frequently regarded as a test of intelligence. It is only when experience has taught one the connections between things that he has really learned from it ; and it is only such learning through insight into connections that is the work of intelligence—the mere formation of habits, even the acquisition of skill through mere repetition need have nothing to do with intelligence.
The apprehension of connections is a distinctive conceptual activity marked by greater spontaneity and originality than are other kinds of cognitive processes, such as sensibility, retention, and even imagination. But it depends upon all these functions for the supply of its raw materials. Similarly, though the appre hension of connections is different from, and superior to, the apprehension of other relations, yet it is usually out of the per ception of these other relations (of similarity and difference, of space and time) that there emerges the apprehension of con nections. The transition may be illustrated, at the lower level of intelligence, from one of W. Kohler's experiments with a chimpanzee called Sultan (see The Mentality of Apes, Eng. trans. p. 8 seq.) . A long string was tied to the handle of a small open basket containing bananas, and pulled through a ring in the wire roof of the animal's playground so that the basket was suspended about 2 metres above the ground ; the free end of the string, tied into a wide, open loop, was laid over a tree-branch about 3 metres distant from the basket, and about the same height from the ground. Sultan was then let into the playground. The animal first looked at the basket, then made for the tree, and climbed up to the loop. Watching the basket, he pulled the string till the basket bumped against the ring in the roof, and repeated the action until the basket turned over and a banana fell out. Thereupon he got down and took the banana. It looks as if the monkey, perceiving the spatial continuity between the rope and the bananas, had some dim apprehension of their connection, and acted accordingly. But even at the highest level of human intelli gence, it is the perception of the other simpler relations that affords the clues to the apprehension of connections. The so-called methods of induction and the other methods of science are mainly based upon such clues.
Intelligence varies enormously in two respects, namely, in degree and in range, or in intensity and in extensity. As regards degree or intensity there must be innumerable grades between the dawning intelligence of a chimpanzee and the ripe intelligence of a great thinker. In the former case the awareness of a connec tion between certain things is probably too dim and vague to be described as more than a feeling; in the latter case it is clear and explicit. Intimately connected with these differences, perhaps only another aspect of them, are differences in what may be called degrees of analysis or freedom, that is, differences analogous to those between "tied" and "free" images. At the lower levels of intelligence, the connections are not yet distinguished from the terms connected, but are fused with them in one concrete situation. At the higher levels of intelligence, the connections are distinguished from their terms, and different kinds of con nection may be tentatively applied to certain objects or events in order to explain them—as happens in all cases of rival hy potheses. Then, again, there are differences in the range of facts which intelligence colligates. A chimpanzee may only be able to deal with a very few facts at a time, and with these only in so far as they constitute one concrete situation. The great thinkers have attempted to colligate the infinite variety of things in one system or cosmos. And there are obviously innumerable intermediate grades possible. Differences in respect of range of intelligence are no doubt intimately connected with differences in degree or intensity, for a higher degree of intelligence stimulates an interest in a wider range of facts.
The discovery of orderliness in natural phenomena has often been regarded as evidence of the existence of some kind of pervasive intelligence in Nature. In one form or another, such a view was held by Anaxagoras, Heraclitus and the Stoics, among ancient philosophers, and by Maimon and Schelling in modern times. The whole idealistic movement in ancient and modern philosophy has, no doubt, been influenced to some extent by the thought that cosmic order presumes cosmic intelligence. In addition to these ontological speculations concerning the objective subsistence of intelligence in Nature, there are, of course, also speculations affecting the theory of knowledge. It has been argued that since connections are not perceived, but only con ceived by the intellect or our intelligence, therefore there is no reason for assuming that there are any real connections among natural phenomena. Science should, therefore, confine itself to mere description, and say nothing about alleged connections. Connectedness or orderliness may be something which the human mind fancifully reads into the phenomena of Nature. Some, indeed, have gone so far as to maintain that the alleged discovery of connection or orderliness among natural phenomena is merely an artistic fancy, a veil of Maya, by means of which the human intellect at once decorates its environment and veils those brutal features which would make life unbearable. Others, again, would admit that the orderliness of Nature is indeed the work of in telligence, and that we consequently know nothing about things in themselves, though we may entertain certain beliefs about them in so far as the moral life of man seems to presume them. Perhaps the most reasonable philosophical conclusion one may draw from the development and survival of human intelligence is that there really are connections in Nature, otherwise our intelli gence could hardly be an instrument of life, such as even the agnostics and the sceptics maintain that it is. It seems more reasonable to suppose that human intelligence discovers useful connections than that it invents useful delusions—however limited its powers may be.
BIBLIOGRAPHY.-See articles INTELLIGENCE TESTS ; ABILITIES, GENBibliography.-See articles INTELLIGENCE TESTS ; ABILITIES, GEN- ERAL AND SPECIAL ; PSYCHOLOGY ; papers by H. W. Carr, A. Wolf, and C. Spearman on "The Nature of Intelligence," in Philosophy and Metaphysics (Aristotelian Society, supplem. vol. v., 1925) ; C. Spear man, The Nature of Intelligence (1924)• (A. Wo.)