The subject of "substance" in Aristotle's work entailed two questions. One question concerned the topic of change while another question entailed the topic of identity.
Regarding the topic of change, Aristotle acknowledged that in our encounters with reality we inevitably encounter change. Leaves on the trees change. Bugs change. Children are born, grow, mature and age.
Aristotle, therefore, became concerned with the "it" that remains the same in the midst of these changes. He readily acknowledged that there is something within the "it" that grows, withers, and dies but he was concerned with that element or those elements that are continuous in the midst of these changes.
He searched for something upon which we could anchor our discourse about change. Aristotle was concerned with the attributes that remain, which do not change, which continue to exist in the midst of change and transformation.
Regarding the topic of identity, Aristotle was concerned with the question concerning the properties that the individual, for instance, possesses that are more fundamental than those properties that transform and change. He engaged in a search for that property or those properties that I must have in order to be myself.
What are the attributes which remain or which do not change or which continue to exist in the midst of the observable changes of my life?
These two issues, change and identity, were intimately connected for Aristotle. Early natural philosophy seemed to be concerned with the nature of matter. It asked concerning the persistent "stuff" or animals, children, trees. Therefore, early natural philosophy had concluded that since when these things "die" matter remains then this must be the underlying identity that he proposed was matter, in short, the stuff of life.
This was an ancient turn on the contemporary idea of reductive materialism.
On the other hand, those of the Platonist school focused on the identity question in a different manner. They attempted to explain identity in terms of relations to immaterial objects that are found in an unseen world, the world of forms or ideas. Each element of one's identity has a matching or corresponding eternal reality in the world of forms. The color brown, the dog, the human, all of these has their corresponding perfect and eternal reality in the unseen Platonic world of forms.
Aristotle however differed with these Platonic conclusions.
He argued for instance that "brown" is "on me", so to speak, and I can lose it without ceasing to be myself.
"Humanness" is different, however.
One quality, brown, is a non-essential quality.
The other quality, humanness" is an essential quality.
In addition, Aristotle also responded to the materialists. He advanced the idea that rather than "humanness" being a "stuff" or "material composition" rather "humanness" consists of an order which exists in the midst of the structure.
He called this the "form" though not in the sense of which Plato spoke of "forms".
Aristotle advanced that idea that Eddie Carder, for instance, is organized to function in a certain way and that this is required for me to exist as Eddie Carder.
For Aristotle, this was true for three reasons:
1. Aristotle reminded that matter is always changing. Socrates cannot be identified exclusively with the matter that composes his body since this matter is constantly changing; yet Socrates remains the same Socrates despite the changes.
2. Aristotle proposed that what he terms the "conception of the artifact" remains the same despite change or alterations. For example, we could take a ship and replace certain parts, but the functionality of the ship remains the same. It is therefore the same ship.
3. Aristotle concluded that matter is not definite to be utilized in a description of the continuity of identity. Matter is only a heap of stuff and is not to be equated with form or function according to Aristotle
