Comma usage in complex sentences.

Happy Halloween!  Today we continue our discussion of punctuation marks—turning our attention to comma usage in complex sentences.   

A complex sentence consists of one independent clause and one or more dependent clauses.  An independent clause is a group of words made up of a subject and a predicate.  By itself, an independent clause is a simple, stand-alone sentence (e.g., “If you build it, he will come.”).  A clause is dependent when it is introduced with a subordinating conjunction (e.g., “because,” “although,” “if,” “after,” “before,” “until,” “since,” “so that,” “unless,” “while,” “when,” “where,” “even though”) or relative pronoun (“who,” “whom,” “whose,” “whoever,” “whomever,” “that,” “which”).

Whether to use a comma between an independent clause and a dependent clause depends upon the meaning of and relationship between the clauses.  When the dependent clause is restrictive—or necessary to the meaning of the sentence—don’t use a comma.  When the dependent clause is nonrestrictive—or not necessary to the meaning of the sentence—use a comma.  (Those rules also explain when to use “that” and when to use “which.”  “That” is restrictive and is used without a comma; “which” is nonrestrictive and is used with a comma.)

Those rules often lead to confusion, because the same sentence can be punctuated more than one way and still be correct, depending on its meaning.

Restrictive:

  • Jack did not make an objection because he wanted to win.  (Meaning:  he objected for another reason.)

Nonrestrictive:

  • Jack did not make an objection, because he wanted to win.  (Meaning:  the reason he did not object was that he wanted to win.)

In some situations, use or omission of a comma can cue the reader about the relationship between two clauses and prevent misreading.  Compare the following examples:

  • Joe’s Helicopters argues that the trial court erred because it presented evidence showing that genuine issues of material fact existed.
  • Joe’s Helicopters argues that the trial court erred, because it presented evidence showing that genuine issues of material fact existed.

In the first example, the “because” clause explains the “that” clause element of the main clause (i.e., why the trial court arguably erred).  By contrast, in the second example, the “because” clause explains the main subject and verb of the main clause (i.e., why Joe’s Helicopters is making the argument).

That is all for now …

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