The estimative power (also commonly, estimative sense) is a power of knowledge whose characteristic act is concrete evaluation or estimation. Spoken of as a distinct power of knowledge first by avicenna, it was accepted as such by the majority of medieval thinkers. Many later authors, however, have rejected it entirely, or have refused to consider it as distinct from the imagination, e.g., F. suÁrez, P. fonseca, and J. frÖbes; others consider it of very little importance, e.g., D. mercier. In Thomistic philosophy, the estimative power is conceived very much as it was by Avicenna (ST 1a, 78.4). It is the equivalent in animals of the cogitative or discursive power in man, though man also in some sense has an estimative power, as explained below.
Nature of the Estimative. A certain intelligence or purposiveness is observable in animal activity, and various explanations, such as instinct, are offered for this. Many accept the explanation offered by Aristotle, i.e., that "animals know by nature" (Phys. 199a 20–30; Meta. 980a 28–981a). Avicenna went further. Having developed an analysis of knowledge in terms of formal objects, he applied this to animal knowledge and activity. He concluded that a distinct power was necessary (Liber Canonis 220.127.116.11; De anima 1.5, 2.1, 4.1, 4.3).
St. thomas aquinas followed this analysis closely, but more briefly. Animals, he asserted, have a knowledge of concrete suitability and harmfulness. Such knowledge is not reducible to the external senses, which know their objects in directly sensible modes. Consequently, this knowledge cannot be explained by the imagination either, whose function it is to retain and reproduce what was previously sensed. St. Thomas calls this knowledge "an unsensed intention" or "knowledge-object not able to be grasped by the [external] senses." Therefore, a distinct power is required. Nevertheless, an animal does not know the nature of good and evil, but only concrete goods and evils which are important to its life and the life of the species (ST 1a, 78.4; De ver. 15.1, 25.2; In 2 de anim. 13). Another aspect of this knowledge is its unlearned, or "natural," character. Hence, the estimative must be determined by nature to judge certain things as good and others as harmful. St. Thomas sees the evidence for this in the fact that animals of a particular species act in the same way (De ver. 24.1, 2; ST 1a2ae, 17.2 ad 3;13.2 ad 2, 3).
Functions in Animal and Man. Because the kind of knowledge reached by the estimative is evaluative, it is immediately ordered to appetite and thus to action (In 3 sent. 27.1.2; De virt. in comm. 6; ST 1a, 83.1). The "good" as known by the animal is concrete and individualized. Consequently, good and evil as thus presented necessarily are followed by acts of appetite: desire, fear, rage, and so on. Hence, the estimative can well be considered to be the guiding, or supreme, power in an animal (In 3 sent. 18.104.22.168.1; ST 1a2ae, 31.6).
To a limited extent, we can speak of an estimative power in man (ST 1a, 78.4). For in the earliest years of human life, reason cannot yet guide actions, and sufficient learning has not yet taken place. If the baby responds to concrete good and evil beyond their immediately pleasurable or painful aspects he can do so only to the extent that he also has natural judgments about good and evil.
The area of animal (and human) behavior explained in thomism by the estimative power is evidently much the same as that explained by instinct. However, the term instinct for St. Thomas is not a technical term, but a general term for "innate" or "intrinsic" impulse. The modern doctrine of instinct is a different kind of explanation and has little in common with the estimative power.
See Also: faculties of the soul; senses; cogitative power.
Bibliography: g. p. klubertanz, The Discursive Power (St. Louis 1952). m. a. gaffney, Psychology of the Interior Senses (St. Louis 1942). r. hain, "De vi aestimativa et de instinctu animalium," Revue de l'Université d'Ottawa 2.2 (1932) 98–114. d. de vorges, "L'Estimative," Revue néo-scolastique 11 (1904) 433–454. h. a. wolfson, "The Internal Senses in Latin, Arabic, and Hebrew Philosophic Texts," Harvard Theological Review 28 (1935) 69–133.
[g. p. klubertanz]