"Quiddity" is Anglicized from "quidditas," which is in turn Latinized from τὸ τί ἦν εἶναι, "the what it was to be," of Aristotle, where that phrase is the same as "essence." Aquinas in SCG I.21.1 talks about essence, quiddity and nature as though they are synonyms.

Form seems interchanged with essence at ST 1a 67.3 c. It gets hazy in both Aristotle and Aquinas to mark exactly how essence and form are and are not the same. Feser writes this in Scholastic Metaphysics, 211:

"The essence of a thing is its nature, that whereby it is what it is. It is what we grasp intellectually when we identify a thing's genus and specific difference.... 

... a material thing's substantial form was characterized as its nature. The point was to emphasize that that by virtue of which a material substance carries out its distinctive activities is something immanent to it rather than either imposed by artifice or the result of accidental circumstances. In a broader sense, however, the essence or nature of a stone, tree, dog, or other material substance includes both its form and its matter, since matter is essential to the operations such things carry out by virtue of their substantial forms. The essence or nature of an immaterial substance, however, would be identical to its form."

 

RomanJoe wrote:

IOW form--in physical beings--is that by which indeterminate matter takes on a determinate nature, operating according to this nature and becoming a certain kind of thing.

Basically, yes. Prime matter is the substrate of substantial change, and secondary matter, of accidental change. Feser in the Blackwell Companion to Substance Dualism says there is prime matter, abstracted from all qualities, pure potentiality, and secondary matter, which has some form or other. This distinction corresponds to that between substantial form, which makes prime matter into a substance, and accidental form, which merely modifies some secondary matter that already has substantial form. Cf. ST 1a 76.8 c: an accidental form, like that of a house, does not give existence to every part of the whole but is a composition and order of the parts; substantial form is of the whole qua whole and thus configures each part too.
 Then there is materia intelligibilis, not "real" in a thing but in the mind when we think about something, as in the definition of quantity, and materia mathematica, or the "matter" of mathematical entities, ST 1a 85.1, esp. ad 2.

The essence is the entirety of the being, including the form (that which determines matter to be a something or other) and matter. Is this roughly right?

I think you might mean by "entirety of the being" the substance rather than the essence. The substance is Socrates; the essence is what Socrates is, i.e. a man. "essence is the definable nature of the thing that exists" (Gaven Kerr). But the essence is of a substance that is a composite of form and matter. The being is an "ens," and it has an essence, "essentia." I might be misunderstanding your phrase, "the entirety of the being," but I wouldn't say that "the essence is the entirety of the being" because that sounds as though the essence and the existence are going to wind up identical - which we know Aquinas says is true only of God.
 

Ficino
Perhaps I worded that last bit wrong. I mean the essence is that which takes account of both form as the actualizing principle of matter and matter--that is, the essence encapsulates both matter and form.

Last edited by RomanJoe (6/04/2018 4:46 pm)

Take a look at the opening paragraphs of De Ente et Essentia. In particular:

6. … the word “essence” must signify something common to all natures, by means of which (nature) diverse beings are placed into diverse genera and species; as, for example, humanity is the essence of man, and so with other things.

7. And because that by which a real thing is constituted in its proper genus or species is what is signified by the definition expressing what the real thing is, philosophers sometimes use the word “quiddity” for the word “essence.” This is what the Philosopher often calls what something was to be, i.e., that by which it belongs to something to be what it is.

8. It is also called form, in the sense in which the word “form” signifies the full determination of each real thing, as Ibn-Sînâ says in the second book of his Metaphysics.

9. Further, it is given another name, nature, taking the word “nature” in the first of the four ways given by Boethius in his book On the Two Natures. In this way, whatever can in any way be grasped by the intellect is called a nature. For a real thing is not intelligible except through its definition and essence.

10. The Philosopher, too, says in the fifth book of the Metaphysics that every substance is a nature. But the word “nature” taken in this way appears to signify the essence of a real thing according as it has an ordering to the thing’s proper operation; and no real thing lacks a proper operation.

11. The name “quiddity,” however, is taken from the fact that what is signified by the definition is the essence. But it is called essence from the fact that through it and in it a real being has existence.

...

14. In composed substances there are form and matter, for example, in man soul and body.

15. But we cannot say that either one of them alone may be said to be the essence. …

16. Neither can the form alone of a composed substance be said to be its essence, although some try to assert this. For it is evident from what has been said that essence is what is signified by the definition of a real thing. And the definition of natural substances contains not only form, but matter as well; otherwise natural definitions and mathematical ones would not differ.

17. Neither can it be said that matter is placed in the definition of a natural substance as something added to its essence or as something outside its essence, because this mode of definition is proper to accidents, which do not have a perfect essence. This is why accidents must include in their definition a subject which is outside their genus. It is clear therefore that essence includes matter and form.

18. Further, neither can it be said that essence signifies some relation between matter and form or something added to them, because this would of necessity be an accident or something extraneous to the real thing, and the real thing would not be known through it. And these are traits of essence. For through the form, which is the actuality of matter, matter becomes something actual and something individual. Whence what supervenes does not confer on matter actual existence simply, but such an actual existence; as accidents in fact do. Whiteness, for example, makes something actually white. Whence the acquisition of such a form is not called generation simply, but generation in a certain respect. It remains, therefore, that the word “essence” in composed substances signifies that which is composed of matter and form.

John West wrote:

RomanJoe wrote:

The essence is the entirety of the being, including the form (that which determines matter to be a something or other) and matter. Is this roughly right?

You're almost right.

There is, for Aquinas, a distinction between Socrates and existing Socrates. Socrates is the essence of Socrates; existing Socrates is the essence of existing Socrates. The remainder when you subtract Socrates from existing Socrates is the essence of Socrates's existence, and how exactly you cash that out is going to depend on how you account for existence (and even Thomists dispute about the right way to do that, cf. Miller and Davies). 

But Socrates doesn't exhaust the being existing Socrates, and so Socrates's essence isn't "the entirety of the being" (Socrates, in this case).

In other words, what Socrates is (his essence) is different than his substantial form because form is merely a determining principle of his matter and not a definitional principle of his being. Is this correct?