Communications Tip of the Week
Commas in Compound Sentences
A frequent punctuation error involves insertion of commas in compound sentences or deletion of
unnecessary commas in simple sentences with compound predicates.
Whoo! Do you find those grammatical terms confusing? Hopefully the definitions below will
help clarify confusion so that the punctuation rules will be easier to understand and apply.
Subject
Predicate
Sentence
Clause
Simple Sentence
Compound Sentence
Conjunction
A noun or pronoun that performs the action of a verb in a sentence
The Intranet provides links to employee resources.
The part of a sentence that expresses what is said about the subject
The Intranet provides links to employee resources.
A group of words with a subject and predicate that expresses a complete thought
BCPS is a large school system.
A part of a sentence that has a subject and verb. It may be independent (makes
sense by itself) or dependent (needs another part of the sentence to make sense).
BCPS is a large school system – independent
When a new employee is hired – dependent
A sentence that has one clause
Employees register for workshops in the Online Registration System.
A sentence that has two or more independent clauses
The workshop is listed in the Workshops–Registration catalog, and
registration opens on December 1.
A connecting word – in compound sentences, the conjunctions are for, and, nor,
but, or, yet, so (remember FANBOYS).
Now to the punctuation rule: Use a comma to separate two independent clauses (complete thoughts)
joined by one of conjunctions listed below (the FANBOYS):
For
And
Nor
But
Or
Yet
So
Look at the examples below. The first is a compound sentence (two independent clauses joined by a
coordinating conjunction). The two clauses could stand alone as separate sentences. The second
example sounds similar, but the words after and do not form a complete thought; therefore, a comma is
not used. (The second sentence is a simple sentence with a compound predicate.)
Department of Professional Development
Communications Tips of the Week/jm
11/2/11
Tip 4 – Commas in Compound Sentences
AandM\Written Comm\Tips of the Week
 The secretary noticed a small discrepancy in the figures, so she decided to review the
spreadsheet.
 The secretary noticed a small discrepancy in the figures and decided to review the
spreadsheet.
Sometimes a sentence without two complete thoughts seems to need a comma before the second verb,
usually when the sentence is lengthy. In this case, consider rewriting the sentence as two sentences.
For more information commas in compound sentences, check out Sections 126 and 127, pages 19–20,
in The Gregg Reference Manual.
Department of Professional Development
Communications Tips of the Week/jm
11/2/11
Tip 4 – Commas in Compound Sentences
AandM\Written Comm\Tips of the Week