To write well, it helps to understand how sentences are structured. Here, we’ll look at compound predicates and how they differ from compound sentences.
What Are Compound Predicates?
Every full sentence (or clause) should have a subject and a predicate:
- The subject is the person or thing performing the action of the verb.
- The predicate is the part of the sentence that tells us what the subject is doing or being. This can be just a verb, or it might include extra information (e.g., an object, or a modifier such as an adverb or prepositional phrase).
A standard predicate will have a single main verb or verb phrase. But a predicate can contain more than one verb or verb phrase, all of which describe the same subject. This is known as a compound predicate.
A compound predicate can be as simple as two verbs joined by a conjunction:
The doors creaked and rattled.
Here, for instance, the subject is “doors,” with the verbs “creaked” and “rattled” forming a single predicate (i.e., both words refer to what the doors are doing).
But sometimes a compound predicate can be more complex:
The symphony starts softly, builds to a crescendo, and ends with a flourish.
Here, the predicate contains three verbs (i.e., “begins,” “builds,” and “ends”), but it also contains modifiers that tell us more about the actions they describe.
A compound predicate can contain as many verbs and modifiers as you like. But long sentences can be hard to read, so it’s best to use lengthy predicates sparingly.
Compound Predicates vs. Compound Sentences
Like a compound predicate, a compound sentence will include more than one verb (or verb phrase). But these “compounds” are different in other ways, including in how they should be punctuated. Let’s take a look at the difference.
In a typical compound sentence, two (or more) independent clauses are joined by a conjunction. And to show that they are separate clauses, we add a comma before the conjunction. For instance, we could say:
Sam ate breakfast, and then she walked the dog.
Here, rather than a single clause with a compound predicate, we have two distinct independent clauses (i.e., each clause would work as a sentence by itself). In the first, the subject is “Sam” and the predicate is “ate breakfast.” And in the second clause, the subject is “she” and the predicate is “walked the dog.”
Were we to present the same information as a compound predicate with a single subject, we would not include a comma before “and”:
Sam ate breakfast and then walked the dog.
This sentence contains two verbs (“ate” and “walked”), but both are part of a single clause with a single subject (“Sam”). The phrase “ate breakfast and then walked the dog” is therefore a single compound predicate.
Importantly, if needed, we can break a compound sentence into two simple sentences without changing the wording at all:
Sam ate breakfast. ✔
And then she walked the dog. ✔
Both of these are complete, grammatical sentences. But if we tried to do the same with a compound predicate, the second half would be a fragment:
Sam ate breakfast. ✔
And then walked the dog. ✘
If you’re not sure whether something is a compound sentence, and therefore not sure whether to add a comma, try breaking it down into two distinct sentences.
Proofreading for Grammar
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