Thomas Aquinas, Disputed Questions on Truth (De Veritate)

1. An activity should be ascribed more to the principal cause than to the instrumental cause. But in us the agent intellect is, as it were, the principal cause of the knowledge which is produced in us. But man who teaches another is, as it were, an instrumental cause, furnishing the agent intellect with the instruments by means of which it causes knowledge. Therefore, the agent intellect is more the teacher than another man. If, then, because of what a speaker says we call him the teacher of the one who hears him, the hearer should in a much fuller sense be called his own teacher because of the light of the agent intellect.

2. One learns something only in so far as he acquires certain knowledge. But such certitude is in us by reason of the principles which are naturally known in the light of the agent intellect. Therefore, the agent intellect is especially fitted to teach. We conclude as before.

3. To teach belongs more properly to God than to man. Hence, it is said in Matthew (23:8): "For one is your master." But God teaches us in so far as He gives us the light of reason, by means of which we can judge about everything. Therefore, we should attribute the activity of teaching especially to that light. The same conclusion follows as before.

4. It is more perfect to learn something through discovery than to learn it from another, as is clear in the Ethics. If, therefore, a man is called a teacher in virtue of that manner of acquiring knowledge by which one learns from another so that the one is called the teacher of the other, he should with much greater reason be called a teacher in virtue of the process of acquiring knowledge through discovery, and so be called his own teacher.

5. Just as one is inspired to virtue by another and by himself, so also he gets to know something by discovering for himself and by learning from another. But those who attain to works of virtue without having another as an instructor or a lawgiver are said to be a law unto themselves, according to Romans (2:14): "For when the Gentiles, who have not the law, do by nature those things that are of the law . . . they are a law to themselves." Therefore, the man who acquires knowledge by himself ought also to be called his own teacher.

6. The teacher is a cause of knowledge as the doctor is a cause of health, as has been said. But a doctor heals himself. Therefore, one can also teach oneself.

To the Contrary:

1'. The Philosopher says that it is impossible for one who is teaching to learn. For the teacher must have knowledge and the learner must not have it. Therefore, one cannot teach himself or be called his own teacher.

2'. The office of teacher implies a relation of superiority, just as dominion does. But relationships of this sort cannot exist between a person and himself. For one is not his own father or master. Therefore, neither can one be called his own teacher.

REPLY:

Through the light of reason implanted in him and without the help of another's instruction, one can undoubtedly acquire knowledge of many things which he does not know. This is clear with all those who acquire knowledge through discovery. Thus, in some sense one can be a cause of his own knowledge, but he cannot be called his own teacher or be said to teach himself.

For in physical reality we find two types of active principles, as is clear from the Philosopher. Now, there is one type of agent which has within itself everything which it produces in the effect, and it has these perfections in the same way as the effect, as happens in univocal agents, or in a higher way than the effect, as in equivocal causes. Then, there is a certain type of agent in which there pre-exists only a part of the effect. An example of this type is a movement which causes health, or some warm medicine, in which warmth exists either actually or virtually. But warmth is not complete health, but a part of it. The first type of agent, therefore, possesses the complete nature of action. But those of the second type do not, for a thing acts in so far as it is in act. Hence, since it actually contains the effect to be produced only partially, it is not an agent in the perfect sense.

But teaching implies the perfect activity of knowledge in the teacher or master. Hence, the teacher or master must have the knowledge which he causes in another explicitly and perfectly, as it is to be received in the one who is learning through instruction. When, however, knowledge is acquired by someone through an internal principle, that which is the active cause of the knowledge has the knowledge to be acquired only partially, that is, in the seminal principles of knowledge, which are the general principles. Therefore, properly speaking, we cannot call a man teacher or master because of such causality.

Answers to Difficulties:

1. Although to some extent the agent intellect is more the principal cause than another's teaching, the knowledge does not pre-exist in it completely, as it does in the teacher. Hence, the argument does not follow.

2. A like solution should be given to the second difficulty.

3. God knows explicitly everything which man is taught by Him. Hence, the character of teacher can suitably be applied to God. The case is not the same with the agent intellect, for the reason already given.

4. For the one learning a science, to learn it by discovery is the more perfect way of acquiring the knowledge, because it shows that he is more skillful in the acquisition of knowledge. However, for the one causing the knowledge, it is more perfect to cause it by means of instruction. For a teacher who knows the whole science explicitly can teach it to a pupil more readily than the pupil himself could learn it from his own rather general knowledge of the principles of the science.

5. A law has the same relation to matters of action as a principle has to speculative matters, but not the same as a teacher. Consequently, if he is a law unto himself, it does not follow that he can be his own teacher.

6. A doctor heals in so far as he has health, not actually, but in the knowledge of his art. But the teacher teaches in so far as he has knowledge actually. Hence, he who does not have health actually can cause health in himself because he has health in the knowledge of his art. However, it is impossible for one actually to have knowledge and not to have it, in such a way that he could teach himself.