Aristotle’s writing style at first seems verbose and roundabout. However, as one begins to follow his thought process it becomes clear that he is in actuality extremely precise, and he delivers his thoughts exactly as he wants them to be read. It is amazing to me how concretely he explains his ideas on something so abstract as the soul.
In the first book, Aristotle begins by asking the questions that will need to be answered, and how one should ask these questions, which is a daunting task, to put it lightly. For example, is there any way to quantify soul? What kind of material is it? Is it one body or does it consist of many parts? Aristotle also discusses the possibility of animals having souls, but it should be clarified that soul in this case does not necessarily translate to the soul that a religious person would speak about having. Soul is here looked upon as anything that is separate from the body and mind, but inhabiting that body.
Aristotle finds further complication in his search when he realizes that there seems to be no case where the soul acts on its own, with thinking being the most likely exception, except that thinking requires an imagination(or a brain). He decides that "all the affections of the soul involve a body-passion, gentleness, fear, pity, courage, joy, loving, and hating", so thus far it seems that the soul does nothing independently.
For a time, Aristotle goes into depth about what conclusions his predecessors have reached about the soul. Some had said that the soul is what originates movement. Deomocritus associates the "motes" in the air(what you see when you shine a flashlight in a dark room) with soul. Pythagorus also associates these motes with soul because of their movement on even a calm day. This movement is related, in their minds, to the life of a body because when they are no longer, they can no more uphold this movement. The main idea of these two thinkers and their compatriots is that soul originates all movement and soul alone moves itself. Anaxagoras’ views are similar but different in that he feels that the mind and not the soul sets everything in motion. This correlation of movement and soul led Thales to believe that the magnet had a soul because it moves the iron. Another thinker, Alcmaeon, said that the soul is immortal because of its inherent ceaseless movement.
Also he said that "all things divine" are in constant motion, for example, the moon, stars, and all the heavens.
Aristotle, however, completely disagreed with the fixation on movement. He went as far as to say, speaking of the soul, that "It is an impossibility that movement should be even an attribute of it". Aristotle says that there is no necessity that what originates movement should itself be moved. He believes, rather, that the soul is moved indirectly, such as when a sailor is moved indirectly on a ship. His legs are not moving him, but he does travel. So with the soul, it would move with the body, indirectly, not causing the movement, but is ‘along for the ride’.
One theory proposed and rejected is that the soul is a harmony because "harmony is a blend or composition of contraries, and the body is compounded out of contraries". This, says Aristotle, is absurd because the composition of different parts of the body is vastly dissimilar and this would mean that the body contained many souls, one for each composition, since each composition is a harmony, thereby a soul.
In Aristotle’s time, it was believed that everything consisted of a combination of earth, wind, water, and fire. Many that had discussed soul before Aristotle concluded that the soul was made of all elements because it comes in contact with all elements throughout the body and it was believed that things were composed of everything they "knew".."like is known only by like.."etc. It is a hard concept to grasp but Aristotle refuted this view by saying that the soul by nature must be impassable– but many elements are not impassable– thereefore making those mentioned not capable of being part of the soul.
Aristotle then concludes in the first book that in each of the body parts there are present all the parts of a soul which are all homogenous to each other, but are at the same time divisible.