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Email Grammar and Style: Using Commas

I. Restrictive vs. Nonrestrictive modifiers:

A modifier can be

A) a subordinate clause (i.e., a relative clause beginning with "who," "which," "that"),

B) a coordinate modifier (a noun phrase, a verb phrase), or

C) an appositive (noun).

A modifier is

  1. restrictive if the noun it modifies cannot be identified without it and the sentence does not make sense unless the identity of the noun is specified.
  2. 2) nonrestrictive if the modifier can be removed without injuring the sentence.


  1. If the modifier is restrictive, no commas are needed.
  2. If the modifier is nonrestrictive, do use commas.


1) Other houses which were designed by Frank Lloyd Wright can be seen in Oak Park.

2) The Robie House, which was designed by Frank Lloyd Wright, can be seen in Oak Park.

1) The man towering over the others is my uncle.

2) My uncle, towering over all of us, saw the parade.

1) His first wife Jamie had blonde hair.

2) His first wife, the blonde, was named Jamie.

1) Nathaniel Hawthorne's story "The Birthmark" provokes interesting discussions.

2) In "The Birthmark," the main character, Aylmer, experiments on his wife Georgiana.

II. Coordination vs. Subordination:

A. Coordination joins two independent clauses with a comma and "and, but, or, nor, so, yet." Two coordinated independent clauses make up a compound sentence. Each clause is equally emphasized by the grammar.

Coordinate modifiers, verb phrases and noun phrases, are dependent clauses joined to the main clause by a comma alone; the relationship between the modifier and the main clause is unspecified:

The early Benedictine monks revived agriculture after the collapse of the Roman Empire, recolonizing the land that was deserted, reintroducing industrial techniques that had been nearly lost.

Paying close attention to Louisa's reactions, the psychologist made careful notes during each session.

B. Subordination, joining a dependent clause introduced by "although, because, by, in order to, since, after" or any relative pronoun, "who, whose, whom, which, that" to an independent clause, creates a hierarchy among elements of the sentence and orders experience according to some kind of relationship between them.

By recolonizing the land that was deserted and by reintroducing industrial techniques, the early Benedictine monks revived agriculture.

The psychologist made careful notes during each session by paying close attention to Louisa's reactions.

Rules for punctuating:

A. Place a comma before a coordinating conjunction joining two independent clauses.

B. Commas set off a modifying clause depending upon whether the modifier is restrictive or nonrestrictive.

The man who towers above everyone is my uncle.

My uncle, who towers above everyone, is a nerd.

(Rule:) Place a comma after an introductory subordinate clause; subordinate clauses which follow the main clause do not need to be introduced by a comma unless (Exception:) the subordinating connector functions like a coordinating connector.

R: Although there are many trial marriages, there is no such thing as a trial child.

R: Because there are so many divorces, children suffer.

Children suffer because there are so many divorces.

E: There is no such thing as a trial child, though there are many trial marriages.

E: The supervisor decided to use the new calculator, although she had never used it on a small job.

R: Even though the supervisor had never used it on a small job, she decided to use the new calculator.

R: The supervisor decided to use the new calculator even though she had never tried it on a small job.

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