Animal is an any organic being endowed with both vegetative and sense life, which is not commonly called "man."¹⁹ Also well known from zoology and natural history is the fact that some animals are more perfect than others, and that animals can be classified in distinct categories.

Instinct is an innate disposition which determines the organism to perceive or pay attention to any object of a certain class, and to experience in its presence a certain emotional excitement and an impulse to action which finds expression in a specific mode of behavior in relation to that object." Bittle notes that instinct can be modified to a minor extent, so a bird will use paper or stings for nest-building instead of leaves and twigs. Nevertheless, animal behavior is the concrete connecting of concrete acts to concrete ends.²⁰ Perceptual insight and memory suffice to give an explanation for animal behavior. Everything in animal activity takes place on the sense level, so that the animal is intrinsically dependent on matter.

Estimative power (vis aestimativa), according to St. Thomas, is a cognitive power in man much like instinct. But man perceives useful and harmful things not just in a purely sensory way, St. Thomas calls this sense in man a cognitive power (vis cogitativa) or "particular reason" to distinguish it from intellectual reason.²¹ Cardinal Mercier calls this estimative power "the sense of well-being" (le sens du bien-Ltre). The Scholastics acknowledged a central sense (sensus communis) as a mental power in man to consciously perceive, distinguish and synthesize the objects and operations of the presently active external senses. T. V. Moore combines the estimative power with this central sense into what he calls the "synthetic sense." In man, this estimative power is much weaker, and much less determinative, than instinct in animals.

Man is any member of the species Homo sapiens today, male or female. Man is a rational animal.²² We abstain from any dealing with any early species of man, although some Neo-Scholastics, such as Marcozzi and La Vecchia at the Gregorian University in Rome, include Homo sapiens neanderthalis as truly members of mankind.²³ We also abstain from treating "primitive" tribes, which Grancelli denies have any ideas; Marcozzi gives a list of articles by twenty-two Ethnologists confirming that even "primitives" today have an idea of God and morality.²⁴ We note the Neanderthals and tribal members in the world today to show that all men have a soul substantially equal when the cultural aspects of life are considered.

The sense life of man is evident from the personal experience of everyone.²⁵ Men can see, hear, smell, taste, and touch. In the function of many of these lower senses of man, these senses are very much inferior to the sensitive life of many animals.

The psychic life of man is composed of many activities that complement and complete the sense life of man, which activities are commonly called intellectual or rational.²⁶ At first glance, these psychic faculties appear to be distinct from the sensitive functions. Descriptively, they are the psychological foundation of all the other perfections by which man exceeds the other animals. These acts render man capable of scientific life, artistic life, moral life, social life and religious life.

The essential difference between man and the other animals is the ability of man to operate in a psychic order superior to the order of sense alone. The psychic operations of man cannot be totally reduced to the sensitive order.

Psychic activities of cognoscitive order, which are called intellectual, and which render man capable of all further perfections which make human life superior to the life of brute animals can be concretely enumerated as follows.²⁷ The ability to form universal concepts from material things that are perceived by the senses. The ability to form concepts of supra-sensible things. The ability to perceive multiple relations formally as such. The ability to elicit formal judgments. The ability to form logical reasoning processes. The ability to know oneself and one’s acts by formal reflection, and to be able to attribute these formally to oneself. However, since these functions can differ between various persons, the argument for the superiority of mankind can be restricted to the two more principle intellectual functions of man, which are the universal concept and the concept of relationship.

Person is defined as rational supposit.²⁸ Rational nature is conscious of itself, also through reflection, and so it can also intentionally possess itself; it is also free and therefore ruler of itself and its own acts, which it has and exercises. All supposits are subordinated to persons as an immediate end, and as a means by which a person might attain its proper goal; person is not subordinated to anything as a means, but directly can move to the attainment of its own proper goal.