In Aristotle, What does it mean for something to be predicated?

Question

I am studying Aristotle's views on substance, and in the narratives of his work, the term 'predicated' is used with great frequency, though not at all defined. In Googling the meaning of 'predicated', I get this:

Predicated: 'state, affirm, or assert (something) about the subject of a sentence or an argument of a proposition'

However, I had no idea what 'subject' means, upon research, it seems to be that which is the reason for existence of a sentence i.e a noun for e.g 'sky' in the 'sky is blue', the subject at hand is sky, to which it is blue. Anyway, I could be wrong, and even if not I still don't know what the subject of a sentence of a proposition is or means. I always thought a proposition was a sentence only one with assertion i.e one that is true or false. So all propositions are sentences but not all sentences are propositions. So this just adds to the confusion.

Furthermore, I can't draw up a connection between predicate, and what it means to be predicated. I think a predicate is a proposition with variables, so for e.g instead of 'the sky is blue', you could have 'the n is v' where n = noun, and v = verb. From this, I suppose to be predicated could mean to be variableized? Though am not at all sure.

This is the passage I have trouble interpreting:

Z.3 begins with a list of four possible candidates for being the substance of something: essence, universal, genus, and subject. Presumably, this means that if x is a substance, then the substance of x might be either (i) the essence of x, or (ii) some universal predicated of x, or (iii) a genus that x belongs to, or (iv) a subject of which x is predicated. The first three candidates are taken up in later chapters, and Ζ.3 is devoted to an examination of the fourth candidate: the idea that the substance of something is a subject of which it is predicated. (SEP entry on Aristotle's metaphysics)

On a side note, perhaps the term is just archaic?

Answer 1

A common structure of sentences is that of subject-predicate. The subject is what the sentence is about, and the predicate is what is said about it. Usually the subject signifies an object and the predicate signifies a property.

A few examples should make this clear:

Aristotle is wise (subject = Aristotle, predicate = is wise)

The sky is blue (subject = The sky, predicate = is blue)

Russell likes math (subject = Russell, predicate = likes math)

Predicates can be thought of as open sentences, i.e. sentences with variables. For example,

x is wise

is a predicate¹.

To predicate a property of a subject is just to substitute a subject for the variable in the open sentence that represents that property. For example, to predicate the property of being blue is just to fill in the blank in '___ is blue'. In this case the property of being blue is predicated of something.

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¹ 'is a predicate' is also a predicate.

Answer 2

Predicates

A predicate (prædicare = "to assert") is, according to the Dictionary of Scholastic Philosophy (p. 95),

that which is affirmed or denied of a subject in a categorical proposition.

A proposition is (ibid., p. 99)

a statement making an affirmation or negation

and a categorical proposition is (idem):

one which makes an absolute statement about its subject.

Predicaments

A category or "predicament" is (ibid., p. 17):

the ultimate logical classification of all genera, species, and finite individuals.

Aristotle outlined his ten categories in his Categories.

Here's an example logical classification (ibid., p. 18): These things can be predicated of any changeable being (ens mobile).

Extension

One can distinguish subject and predicate by looking at the extension of the terms. Subjects are of greater extension than that which is predicated of them.

Take "ball" and "red" as an example. The extension of "ball" is much less that that of "red [things]." Thus, "ball" could never be predicated of "[all] red [things]" as in

"[All] red [things]" is "ball."

This would imply the only red things are balls.

But "red" could certainly be predicated of "ball," as in

The ball is red.

This is because "[all] red [things]" has greater extension than "ball."

Further Reading

1. A concise overview: Modern Scholastic Philosophy (vol. 2) pp. 135ff. by Desire Joseph Mercier (pp. 144ff. discuss predication specifically)
2. Ch. II of vol. 1 of Coffey's The Science of Logic is on the predicables.
3. The Scientific Art of Logic: An Introduction to the Principles of Formal and Material Logic (1961) by Edward D. Simmons
4. Outlines of Formal Logic (OFL) and The Material Logic of John of St. Thomas: Basic Treatises by the logician John Poinsot
   ^{Historian of medieval logic Terence Parsons calls, in Articulating Medieval Logic, the OFL by Poinsot "a very competent work from the early 1600s"}

Answer 3

If a property-bearer (anything that can be referred to, even in a Meinongian semantic ontology, has a respectively unique set of nuclear properties) bears certain property(s), then that predicate (the property it bears) obtains of, or is predicated of, the subject (the property-bearer, or thing that bears or has the property). If the sky can bear/have properties, and blue is one such property it could have, and it does have said property, then the sky bears the property blue, typically expressed in a sentence of the form 'X [copula] F,' or 'Sky is blue.' Remember Russell's analysis of the copula (is/are), with the copula typically referring to some condition obtaining of an object, or being something had or attached into the ontological nature or existence-criteria of the individual object, as meaning either (1) composition or makeup (the floor is lava!), (2) quality or feature (the rock is brown), or (3) relation (he is late for work).