About the types of forces, speaking in general

Forces and actions are known one through the other, since every force is the beginning of some action, and every action occurs only from some force. Therefore, we have combined forces and activities in one department. According to doctors, there are three kinds of forces and kinds of actions resulting from them: the kind of mental forces, the kind of natural forces and the kind of animal forces. Many of the philosophers and all doctors, especially Galen, believe that for every force there is a dominant organ; he is the seat of this force, and the actions it produces emanate from him. Proponents of this opinion believe that the seat of mental force and the source of its actions is the brain and that natural force has two varieties. The purpose of one of them is the preservation of the individual and its regime. This power directs the matter of nutrition and nourishes the body while it exists, and also grows it until the time its growth ends. The location of this species and the source of its action is the liver.

Another variety aims to preserve the species. She manages the matter of reproduction and separates the substance of the seed from the mixtures of the body, and then gives it an image with the permission of her creator. The seat of this species and the source of its actions are the testicles.

Animal force organizes the work of pneuma, which is the bearer of sensation and movement; it prepares the pneuma to receive them when the pneuma arises in the brain, and makes it capable of entering the body in which life spreads. The seat of this force and the source of its action is the heart.

As for the worthy sage Aristotle, he believes that the source of all these forces is the heart, but these mentioned sources serve for the manifestation of their primary actions.

Also, the beginning of sensation, according to doctors, is the brain, and then for each of the five senses there is a separate organ from which the action of sensation is manifested.

However, if one investigates and checks, as it must of necessity, it will turn out that things are as Aristotle thought, and not those people, and the statements of these latter will turn out to be extracted from premises that satisfy them, but are not necessary, and it will turn out that they In this case, only the appearance of things is followed. However, the doctor, since he is a doctor, is not obliged to find out which of these cases is true - this rests with the philosopher or natural scientist. A doctor, if it is indisputable for him that the mentioned organs are certain sources for these forces, should not know, during his practice of medicine, whether these forces were previously drawn from another source or not, whereas a philosopher is not allowed not to know this.