Question: How does Aristotle answer the fundamental ontological question,” What are the basic realities (ousia/ substance)? How does his answer differ from Plato’s?
Aristotle’s explanation was that there are two basic kinds of ousia: primary substance and secondary substance. Then, there are other kinds of things that pertain to these. Primary substances, according to Aristotle, are those things which are neither said of (asserted of), nor present in, a subject. That is, individual things, e.g. this man, this ox, this snake, this tree… etc. These ‘individual’ things require sentience; they need both a nutritive and a reproductive soul. Due to the presence of a reproductive soul, they must also be able to reproduce their own kind. Further, they must be of natural kinds, id est things given by nature. They must be identifiable (separate) and re-identifiable (capable of taking on contraries). Here, Aristotle is stating, contrary to Plato, that these primary substances ARE the things themselves, whereas Plato asserted that these things were composites of forms beyond themselves. So, according to Aristotle, the form ‘ox’ isn’t present in ‘this ox,’ neither is the ox participating in the form ‘ox,’ but the ox is an ox, and therefore the universal ‘ox’ exists. ‘This ox’ isn’t said of the universal ‘ox,’ however, because it isn’t all ‘ox.’
Primary substances are those things of which everything is predicated, but which are not predicated of anything. In other words, the 'universal' [man] is predicated by the existence of things like Socrates, but the universal [man] does not necessitate the existence of the man Socrates. This brings us to the secondary substances.
The secondary substances, according to Aristotle, are ‘said of’ a subject, but not ‘present in’ a subject. For example, take the sentence,” Socrates is a [man].” Socrates is obviously the primary substance (this man) and so [man] is the secondary substance. Socrates is a man; [man] is said of Socrates. But, ‘Socrates’ isn’t said of [man]… otherwise, we would all be Socrates! So, Socrates is being (ontologically) a man. He is a man, but [man] is not Socrates.
I had said that there were other kinds of things which pertain to primary and secondary substances. Aristotle said that one of these other kinds of things, were 'in' individuals in categories other than substance. Of these he said that they are ‘in a subject,’ but not said of any subject. The example Aristotle gives is ‘knowledge of grammar’ and it is easy to see what he means here. The knowledge of grammar is ‘in’ Socrates, but no one would say that Socrates ‘is’ the knowledge of grammar. So, these things are an entirely different substance than ‘ox’ or ‘this ox.’
The other kind of things that pertain to primary and secondary substances are those things which are both ‘in’ and ‘said of’ subjects. This idea has recourse to Aristotle’s belief that things are the primary basis. What I mean is, or rather what Aristotle means, is that the primary things are necessary to these things. An easy example is that I am blond. ‘I’ predicate ‘blondness,’ but blondness does not predicate me. [Blond] exists because individual things that are blond exist. Blond is both said of me and in me.
All of these ousia above listed form categories of themselves and develop a taxonomy of quantities, qualities, relations, and places. So, for example, if you have the primary substance (individual) of Socrates, the next thing is up the teleology is the species [man]. Then, above that is the genus [animal]. And above that would probably be [being] and it wouldn't go any higher, because being is being; it's not a composite of universals like Socrates, man, and animal are.
Aristotle also classifies these substances according to their causes, of which there are four. These causes are teleological explanations and therefore pertain to teleology and the nature of the substances. The first cause is ‘that out of which a thing is made and which remains after the change;’ this is the 'material cause,' e.g. the metal out of which a hammer is made. The second cause is ‘that into which a thing is made;’ this is the 'formal cause,' e.g. the hammer itself. The third cause is ‘that by which a thing is made;’ this is the 'efficient cause,' e.g. the blacksmith who made the hammer. The fourth cause is ‘that for the sake of which a thing is made;’ this is the 'final cause,' e.g. the hammer was made for pulling nails and pounding them in. So, according to Aristotle, there is a teleological explanation for everything.
Now, Plato’s ideas differ from Aristotle’s. Aristotle does a good job of explaining the difference in the sixth chapter of the Metaphysics. He points out that Socrates was in pursuit of what Aristotle termed ‘universals of ethics’ instead of the things themselves, i.e. ethical things. Socrates was looking for [virtue] and not virtuous things. Plato took this pattern of pursuit and applied it to all the things themselves. For Aristotle, universals were bi-products of individual things. For Plato, individual things were the bi-products of universals, and the individual things weren’t really individuals, rather, they were composites of what Plato called 'forms.'
So, for a working example: Aristotle would say that heroism exists because individual things are heroic, and white exists because there are white things, and that the individual man is the predication of these things. Plato, however, would say that the body is merely organon (a tool or a vessel) which participates in the ‘form’ of heroism, and the ‘form’ of whiteness ‘itself.’ Further, because of this difference, they disagreed on the concept of 'flux' which originated with the Heracleiteans. For Aristotle, primary and secondary substances were always in a state of flux because they were taking on contraries at varying rates. For Plato, the organon of matter was simply participating in forms one instant and other forms the next.
So, very basically, Aristotle was a materialist; things were and are, in and of themselves, their own explanation. Plato, on the other hand said that a whole host of other things in and from the 'intelligible realm' were necessary to the existence of sensible things. For Aristotle, the rock is a rock, because it is a rock, and from the individual 'rock' comes the universal [rock] and [gray] and so forth. For Plato, the matter of the rock was participating in the form ‘rock,’ and the form ‘one,’ and the form ‘gray,’ and the form ‘hard.’ Plato’s philosophy multiplied problems by saying that the answers were elsewhere in the intelligible realm, doubling the subjects. Aristotle’s philosophy took the answers out of the intelligible realm and put them back into the sensible and said,” The answer is right here, and there’s no need to multiply the problem.”
"Every art and every inquiry, and similarly every action and choice, is thought to aim at some good; and for this reason the good has rightly been declared to be that at which all things aim." ~Aristotle~