A phrase is a group of words without a subject-verb structure. For example:

in 1979

before the party

Phrases cannot stand alone. Instead, they function as part of a sentence:

In 1979, the Declaration of Independence was 203 years old.

Note that, as an introductory phrase, In 1979 is set off by a comma. But the same phrase, appearing at the end of the sentence, would not be set off in any way:

The Declaration of Independence was 203 years old in 1979.

Why not? If there were a comma before in 1979, the date would seem like an afterthought, a bit of nonessential information. But in fact, it is essential. The sentence would seem incomplete— meaningless, even— without it.

What about phrases that appear in mid-sentence? Do they require commas? Consider these examples:

Nobody in this class got better than a B+.

He stood outside, his hands in his pockets, waiting for a friend.

In the first example, the phrase in this class is essential; without it, "nobody" could mean "nobody at Case Western Reserve University" or "nobody in the world." That's why the phrase appears without commas. In contrast, the phrase his hands in his pockets does not seem critical to the meaning of the second sentence, so commas are appropriate.

Admittedly, the phrase his hands in his pockets could turn out to be critical: maybe the man is concealing a gun. Still, the wording and structure of the sentence make the commas a necessity. Without them, the sentence would be difficult to read.

Analyzing Sentences

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