Per se unity 2

Here are some more thoughts on 'per se unity'. I had a post on this earlier.

For Aristotle, change occurs when a subject x acquires a form F. There are, however, two broad types of change: substantial change, and accidental change.

In substantial change, the subject is a lump of matter, and the form is a substantial form. The matter and substantial form together constitute a substance (e.g., Socrates' matter and a substantial form constitute the human person Socrates).

In accidental change, on the other hand, the subject is a substance, and the form is an accidental form (e.g., when Socrates goes to the beach and gets a tan, Socrates is the subject, and his tan color is an accidental form).

According to Aristotle, matter and a substantial form have 'substantial unity' (or 'per se unity', as it's also called), and a substance and its accident has 'accidental unity'. And for Aristotle, the constituents in a substantial unity are tied together much more tightly than those in an accidental unity. For instance, the matter and form in Socrates are tied together more tightly than Socrates and his tan color.

But as far as I can see, it's very difficult to identify the precise way that a substantial unity is tighter than an accidental unity. In both cases, the constituents are related to each other in many of the same ways. Consider the following.

(1) In both cases, the subject can survive the gain and loss of the form. For instance, Socrates can lose his tan, but Socrates' matter can likewise lose his human form.

(2) In both cases, the form can only exist by inhering in a subject. An accident like a tan color can only exist when it inheres in a subject (like Socrates), but Aristotle thinks that applies to substantial forms too: Socrates' human form can only exist when it inheres in a lump of matter.

(The Christian scholastics believe human forms can survive the death of their bodies, but that's a special case. We can easily use a different example to make the same point: even the Christian scholastics believe that Beulah the cow's substantial form can only exist in a lump of matter.)

(3) In both cases, the identity of the composite depends on the identity of its constituents. For Aristotle, Socrates would be destroyed if his matter and form were separated, but 'tan-Socrates' also cannot survive if its constituents are separated: 'tan-Socrates' ceases to exist when Socrates loses his tan.

(4) In both cases, the subject and the form are related in terms of potentiality and actuality. For instance, Socrates' matter has the potential to have a human form, and Socrates' human form actualizes that potential. Likewise, Socrates has the potential to be tan, and his tan color actualizes that potential too.

So for both accidental and substantial unities, the form actualizes a potential in the subject, the form can only exist by inhering in the subject, the subject can survive the loss of the form, and the subject and the form together constitute a unity that cannot survive if the subject and the form are taken apart. In what way, then, are substantial unities 'tighter' than accidental unities? I don't know.

It's tempting to say that while Socrates' tan color is tied to Socrates only 'accidentally' (i.e., 'loosely'), a human substantial form is tied to Socrates essentially (i.e., much more 'tightly'). But this does not help, for it equivocates on the meaning of 'Socrates'.

When we say the tan color is accidental to Socrates, we are taking Socrates as the subject of the tan color. But when we say a human substantial form is essential to Socrates, we are taking Socrates as the composite of a subject (matter) and a form.

Thus, although Socrates is the subject of his tan color, Socrates is not the subject of his substantial form. Rather, Socrates' matter is the subject of his substantial form. So while it's true that Socrates' tan color is accidental to its subject (Socrates), it's also true that Socrates' human form is accidental to its subject (Socrates' matter).

Similarly, although Socrates is the composite of which his substantial form is an essential component, Socrates is not the composite of which his tan color is an essential component. Rather, 'tan-Socrates' is the composite of which the tan color is an essential component. So while it's true that Socrates' human form is an essential component of the composite Socrates, it's also true that Socrate's tan color is an essential component of the composite 'tan-Socrates'.

Thus, we need to be careful when we talk about how constituents are 'essential' or 'accidental' to their subjects and/or composites. In both cases, the forms are accidental to their subjects, but essential to their composites.