Subjects and predicates

Calling syntax ‘the grammar of sentences’ is all very well, but sentences prove as difficult to define as ‘words’ did. We are used, in literate societies with a written-language bias, to thinking of a sentence as something that generally begins with a capital letter and ends with a full stop, but this does not get us very far. A traditional definition of a sentence as ‘the expression of a complete thought’ is not helpful either: are elderberry drink, exactly or good! not ‘complete thoughts’? In traditional grammar, sentences were required to have a subject and a predicate, i.e. something we are talking about (the subject) and then something said about it (the predicate):

1 Dinosaurs existed.

2 Samantha is preparing for her bar examinations.

3 Paul gave a tip to the waiter.

Identifying the subject in Latin, Russian or Polish would be straightforward, because the nouns would be case-marked, i.e. inflected according to their function in the sentence. This is no longer true of English (though it used to be), but pronouns – with the exception of third-person singular it – do retain case-marked forms, so we can apply a substitution test. Thus in the list above, the subjects are Dinosaurs, Samantha and Paul, because they alone can be replaced by subject (or nominative) forms (they, she and he respectively). In traditional grammar, everything else in the sentence is the predicate.

There is nonetheless something unsatisfactory about this definition. Sentence 3, for example, simultaneously ‘says something’ about Paul, a tip and the waiter: why should we prioritize Paul among these? With the appropriate intonation, the focus of the sentence could be shifted to a tip (e.g. as a response to ‘What did Paul give the waiter?’) or to the waiter (in response to ‘To whom did Paul give a tip?). Linguists and logicians would call Paul, a tip and the waiter in sentence 3 arguments, and define predicate more narrowly as expressing a property of an argument, as in sentence 1, or a relationship between arguments, as in sentences 2 and 3. A well-formed sentence must contain a predication.

The predicates in the sentences above are of three different kinds:

In sentence 1, the single argument dinosaurs is the subject, and the predicator is the intransitive verb exist, which allows no other complements.

Sentence 2 has both a subject (Samantha) and a direct object complement (her bar examinations), because the verb prepare has both an agent (doing the action) and a patient (something on the receiving end of the action).

Sentence 3 has a subject (Paul), a direct object (a tip) and an indirect object (the waiter).