Predicates are the things which tend to cause most problems when deciding the correct case for pronouns, e.g. I or me, he or him, who or whom.
This is the definition of 'predicate' in the Ox. Dict.
(grammar) a part of a sentence containing a verb that makes a statement about the subject of the verb, such as 'went home' in 'John went home'.
CMOS doesn't have a definite of 'predicates', only of 'predicate adjectives' at 5.81 which I've quoted below.
Note the other thing that can be a predicate is a noun/pronoun. That's what I'm mostly interested in here, because it is personal pronouns (and who, whom, …) which cause so many grammar problems for whether they should be in the nominative (aka subjective) case or the objective case.
This is CMOS 5.81, its definition of 'Predicate Adjective'
A predicate adjective is an adjective that follows a linking verb (see 5.99) but modifies the subject [the child is afraid, the night became colder, this tastes delicious, I feel bad].
If an adjective in the predicate modifies a noun or pronoun in the predicate, it is not a predicate adjective. For example, in 'the train will be late' the adjective 'late' modifies the subject 'train'. But in 'the train will be here at a late hour' the adjective 'late' modifies the noun 'hour', not the subject 'train'. So even though it occurs in the predicate, it is not known as a predicate adjective, which by definition follows a linking verb.
I hear more moaning, "WTF is a linking verb?"
It's also known as a 'copula verb' or 'connecting verb'.
More moans. Okay, if you insist, here's its definition of a 'linking verb' at 5.99.
A linking verb (also called a copula or connecting verb) is one that links the subject to an equivalent word in the sentence — a predicate pronoun, predicate noun, or predicate adjective.
The linking verb itself does not take an object.
There are two kinds of linking verbs:
- intransitive verbs that are used in a weakened sense, such as seem, smell, appear, feel, and look. When used as a link, the weakened intransitive verb often has a figurative sense akin to that of 'became', as in 'he fell heir to a large fortune (note: he didn't physically fall on or into anything) or the river ran dry (Note: a waterless river doesn't run, it just dries up). See5.167.
So, just when you've gotten used to the idea a sentence has a subject and a verb and usually some object(s), I come along and say, "That's not quite so." If the verb is the be-verb, or a linking verb, then it usually has a predicate, not an object, whenever it's providing some description of or identifies the subject of the sentence.
The predicate may be an adjective (phrase) or a 'substantive' (which means any noun, pronoun, or phrase serving the function of a noun). It cannot be an adverb, because that would be modifying the verb. For example, 'badly' is an adverb modifying 'feel' in the sentence 'I feel badly', but 'bad' is a predicate providing a description of the subject 'I' in the sentence 'I feel bad'.
I'll add one more comment before leaving you in peace, or should that be 'in pieces'? The lists of linking verbs I've seen seem quite familiar. They might, I can't be sure, be the same as the 'filter words' we discussed recently in this thread: