Psychology

From the Catechism of the Summa of St. Thomas Aquinas by Fr. Thomas Pègues:

What is man?
Man is a composite of spirit and body, in whom the world of spirits and the world of bodies in some sort coalesce (LXXV.).

What is the spirit called that is in man?
It is called the soul (LXXV. 1-4).

Is man the only being in the world of bodies that has a soul?
No. Besides man plants and animals have souls.

What is the difference between the soul of man and the souls of plants and animals?
There is this difference, the soul of a plant has only vegetative life, the soul of an animal has both vegetative and sensitive life, whereas the soul of man has in addition an intellective life.

Is it then by intellective life that man is distinct from all other living beings in this world?
Yes

Is this intellective life of the soul of man, in itself, independent of his body?
Yes (LXXV. 2).

Can any reason be given to establish this truth?
Yes; and the reason is because the object of thought is something wholly immaterial.

But how does it follow from this that the human soul in its intellective life is, in itself, independent of body?
This follows because if the soul itself were not wholly immaterial it could not attain by thought to an object wholly immaterial (ibid.).

What follows from this truth?
It follows that the soul of man is immortal (LXXV. 6).

(B)

Can it be shown that the immortality of man's soul follows from this truth?
Yes. Because if in the soul there is an act wholly independent of bodily matter, it must itself be independent of bodily matter.

What follows from this truth that the soul is, in itself, independent of bodily matter?
It follows that if the body perishes by separation from the soul, the soul itself does not perish (ibid.).

Will the human soul live forever?
Yes.

Why then is the human soul united to a body?
The human soul is united to a body in order to make a substantial whole called man (LXXVI. 1).

Is it not then accidental that the soul is united to a body?
No, for the soul was made to be joined to a body (LXXVI. 1).

What are the effects of the soul upon the body to which it is united?
The soul gives to the body every perfection that the body has, that is it gives to it being, life, and sense; but thought it cannot give, for this is proper to the soul itself (LXXVI. 3, 4).

XIV. OF THE VEGETATIVE AND SENSITIVE POWERS

(A)

Are there in the soul divers powers corresponding to the divers acts it produces?
Yes, with the only exception of the first perfection which the soul gives to the body, namely, existence; but it gives this not through some power or faculty, but immediately, of itself (LXXVII.).

What powers of the soul give life to the body?
The vegetative powers.

What are these powers?
They are three in number, viz., the power of nutrition, of growth, and of reproduction (LXXVIII. 2).

(B)

What faculties of the soul give sense to the body?
The sensitive powers.

What are these powers?
They are twofold: the powers of knowing and the powers of loving.

What are the sensitive powers through which the body knows?
The five external senses (LXXVIII. 3).

What are these powers called?
They are called the powers of seeing, hearing, smelling, tasting, and touching.

And the five external senses, what are they called?
They are called sight, hearing, smell, taste, and touch (ibid.).

Are there also any internal sensitive powers of knowing that do not appear externally?
Yes, they are the common (or central) sense, the imagination, instinct (or estimative sense), and memory (LXXVIII. 4).

XV. OF THE MIND AND ITS ACT OF UNDERSTANDING

(A)

Are there any other powers of knowing in man?
Yes, there is another faculty of knowing, and it is man's chief power.

What is this chief power of knowing in man called?
It is called his reason or intellect (LXXIX. 1).

Is reason and intellect one and the same power of knowing in man?
Yes (LXXIX. 8).

Why are these two names given to the same power?
It is because in the act of knowing man sometimes understands at a glance as it were without reasoning, whereas at other times he must reason (ibid.).

Is reasoning an act proper to man?
Yes, because of all beings that are, man alone is able to reason, or has need of reasoning.

Is it a perfection in man to be able to reason?
Yes, but it is an imperfection to have need of reasoning.

Why is it a perfection in man to be able to reason?
Because in this wise man can attain to truth; whereas no creature inferior to man, such as animals which are without reason, can do this.

Why is it, on the other hand, an imperfection in man to have need of reasoning?
Because in this wise he attains to truth by slow degrees only, and he is thereby liable to err; whereas God and the angels who have no need of reasoning attain to truth straightway without fear of making a mistake.

(B)

What is it to know truth?
To know truth is to know things as they are.

What then is it not to know things as they are?
It is to be in ignorance or in error.

Is there any difference between being in ignorance and being in error?
Yes, there is a great difference; to be in ignorance is merely not to know things as they are; whereas to be in error is to affirm that a thing is, when it is not, or conversely.

Is it an evil for man to be in error?
Yes, it is a great evil, because man's proper good consists in knowledge of the truth which is the good of his intellect.

Has man a knowledge of the truth at birth?
No, at birth man has no knowledge of the truth; for though he then has an intellect it is in an entirely undeveloped state; its unfolding, necessary for the attainment of truth, awaits the development of the powers of sense which are its handmaids (LXXXIV. 5).

When then does man begin to know truth?
Man begins to know truth when he has attained the use of reason, that is at about the age of seven years.

(C)

Can man know all things by his reason?
No, man cannot know all by his reason adequately, that is if one considers his reason within the limits of its natural powers (XII. 4; LXXXVI. 2, 4).

What things can man know by the natural force of his reason?
By the natural power of his reason man can know all things attainable by his senses and all that these things manifest.

Can man know himself by the natural power of his reason?
Yes, because he himself is a thing attainable by the power of sense, and by the help of other things that fall within the scope of his senses, he is able, by reasoning, to come to a knowledge of himself (LXXXVI I.).