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Descriptive Analysis. The term instinct has been used, both in the scholastic philosophical tradition and by some scientific students of animal behavior, to refer to certain complex animal behavior patterns, e.g., hunting, nest building, and the tending of offspring. In these and similar examples, the complexity of the action is thought to exceed that of a direct stimulus-response or sensationappetition sequence, but to fall short of intelligent or rational foresight and planning. Rough criteria are as follows: instinctive behavior involves the entire organism, not merely an isolated receptor-effector mechanism; it is exhibited with some uniformity by all members of a species (or specific subgroup, e.g., worker bees), and its appearance may be distinctive of the species or group; its performance depends on the appropriate physical maturation, but does not require mimicry, trial-and-error activities, or other forms of learning. Such behavior is almost always adaptive, i.e., of positive advantage to the survival of the individual or its species.

Although these criteria have a rough value, their scientific precision and significance have been seriously questioned. To say that certain behavior patterns are unlearned, species-specific, and adaptive does not distinguish them from the more inclusive metabolic processes. To say that a behavior pattern is innate is to ignore the biological theory that genes, not characters, are transmitted from one generation to the next. The development of an organism's anatomic, metabolic, and behavioral traits involves the interaction of its genetic constitution and its environment; consequently, the distinction of innate and learned behavior patterns is softened to the point that some authors speak of genetically controlled propensities to learn rather than of innate behavior patterns. The prominent borderline phenomenon of "imprinting" is of similar significance. Imprinting is the tendency, e.g., of young birds, for a short, definite interval after hatching, to accept and follow a diverse variety of parent substitutes. Such performances are on the border between learning processes more extended in time and purely innate behavior.

Relation to Vis Aestimativa. In the philosophy of Saint thomas aquinas, the estimative power (vis aestimativa ) is one of four interior sensory powers necessary for the life of a perfect animal. The others are the imagi nation, the central sense, and the memory. Although references such as those to a "perfect" animal seem to give this position a deductive or rationalist tone, relevant factual materials are available for its inductive support:(1) The external sensation of at least some animals is quite like that of men. (2) Animals act with respect to objects that are neither gratifying nor unpleasant to the external senses, e.g., sight, touch, and smell. Birds are said to choose nesting materials that, though not attractive to sight or touch, are appropriate for nest construction, so that the choice serves the survival of that species of birds.(3) Such activities, as exhibited by the members of a particular species, exhibit a degree of uniformity. (4) But they also exhibit some plasticity or variability and are not altogether stereotyped. Consequently, what needs explanation is the order or pattern of the sequence of actions and not any mechanical repetition of identical behavioral elements. (5) The performance of these activities is likely to vary with the seasons and with the organic condition of the animal; it is not an automatic response to an external stimulus.

The interpretive principles employed in the analysis of these data include the following theses: (1) One knows, by observation and analogy, that such behavior flows from knowledge and appetite. (2) In cases in which such behavior cannot be explained by the knowledge gained through the external senses, one may rightly infer the appropriate interior sense. (see senses.)

The various data are consequently explained by the existence of a distinct internal sense power (the estimative) capable of apprehending the concrete usefulness of particular sequences of actions. The power is said to be innately determined (diversely within various species) to recognize certain organism-environment groupings as desirable and others as undesirable. Inasmuch as the proper object of this sense power is the total organism environment grouping, both plasticity and uniformity are accounted for. Similarly included within this proper object is the contemporary state of the organism itself, so that the dependence of instinctive activity upon seasonal and individual variations in metabolic state also is explained.

Critical Evaluation. The explanatory value of such statements as "the bird returned to its nest because of its homing instinct" and "the sheep flees the wolf because its estimative power is innately determined to recognize that particular organism-environment grouping as undesirable" have been called into question by students of scientific methodology. One important objection is that such explanations are really uninformative tautologies, i.e., they simply reformulate the data they pretend to explain. What is a homing instinct? If the philosopher can give no other answer than "the power by which the bird returns to its nest," the criticism seems accurate.

Another way of putting this criticism is to ask for some additional means of confirming the presence of a "homing instinct," or an "estimative power." Philosophers who hold a generally Thomistic position tend to reply with a negative argument, viz, one showing that instinctive behavior cannot be explained in terms of tropisms or reflexes and thus must be accounted for by the estimative power or some analogue for it. The formal requirements for an argument of this sort are impressive; e.g., it must be shown that the alternatives considered exhaust all possible alternatives. Argumentative rigor of this level has not actually been sought in past discussions of this topic. However, a number of interesting points have been made in illustration of weaknesses of any "mechanistic" explanation of animal behavior: (1) Reflex behavior lacks spontaneity or autonomy; it is controlled by outside stimuli. Reflex action exhibits a mechanical, off-on, relation to outside stimulation, rather than the dependence on internal events characteristic of instinctive behavior. (2) Reflex action is stereotyped or invariable in form, and so incapable of explaining the adaptive plasticity of instinctive behavior. Reflex behavior shows no tendency to improve with repeated performance as do many forms of animal behavior. From this sort of evidence it is argued that animal behavior cannot be explained in terms of a concatenation of neuromuscular reflexes and therefore must be explained in terms of some cognitive or conscious awareness of the form and purpose of the animal's activity, by the animal itself.

This last sort of argument seems to assume, however, that mechanistic theories are themselves invariable in form. In the third quarter of the 20th century, neurologists are not limited to summing the consequences of simple reflex acts, but have demonstrated a variety of facilitating, inhibiting, and correlating neural mechanisms whose activities, in ensemble, are not stereotyped and stimulus bound. At the same time, mechanism of a rigid and parochial sort is nowhere regarded as a philosophically viable explanation of animal behavior. Empiricist schools, which may be the nearest living relatives of past mechanist schools, are in fact critical of mechanism's pretensions completely and dogmatically to solve the problems of animal behavior.

Perhaps the most commendable aspect of the Thomistic explanation of instinctive activity in terms of the functioning of an estimative power is its emphasis on the really novel complexity of the phenomena in question. Instinctive behavior is not a topic on which one expects much illumination from any form of monism or exaggerated dualism. It is not a topic that is emphasized in the philosophies of atomists or Cartesians. Its appearance among the problems considered in the Thomistic theory of knowledge is a tribute to the complexity and richness of this theory, which permits cross-level, nuanced analyses where simple reductionist alternatives would seem to ignore relevant detail and significant form.

See Also: intelligence.

Bibliography: r. g. busnel, ed., Acoustic Behavior of Animals (New York 1963). j. f. donceel, Philosophical Psychology (2d ed. New York 1961). j. j. dreher and w. e. evans, "Cetacean Communication" in Marine Bio-Acoustics, ed. w. n. tavolga (New York 1964). g. p. klubertanz, The Discursive Power (Saint Louis 1952). w. kÖhler, The Mentality of Apes, tr. e. winter from 2d ed. (New York 1926; repr. 1959). a. portmann, Animals as Social Beings, tr. o. coburn (New York 1961). a. roe and g. g. simpson, eds., Behavior and Evolution (New Haven 1958). e. wasmann, Instinct and Intelligence in the Animal Kingdom, tr. from 2d. ed. (Saint Louis 1903).

[a. e. manier]

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