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7.14 Restrictive/non-restrictive

Most difficulties with the use of the comma hinge on the distinction between restrictive and non-restrictive sentence elements. A restrictive word, phrase or clause adds to the words it modifies a "restrictive" or defining element that is essential to the meaning of the whole; it should therefore not be separated by a comma or other mark of punctuation. A non-restrictive element provides incidental or supplementary information which does not affect the essential meaning; it should be set off by a comma or commas.

Compare

  • The senators who had objected most strongly to the shift in policy were quick to acknowledge the error in their thinking. (restrictive)

and

  • The senators, who had objected most strongly to the shift in policy, were quick to acknowledge the error in their thinking. (non-restrictive)

(a) Introductory elements

There are exceptions to the general rule for punctuating restrictive and non-restrictive elements. An introductory phrase or clause, especially if it is a long one, is often followed by a comma even if it is restrictive:

  • Of all election issues, the place of minorities in society is the most sensitive.
  • When choosing between two approaches, it is important to consult experts in the field.

but

  • In the course of the conference some provincial leaders reversed their position on Native rights.

Each of the above sentences could have been correctly punctuated with or without the comma. But an introductory subordinate clause is normally followed by a comma:

  • If you can’t log on the Web site, then call the technical help desk.
  • Now that the Canadian film industry has come of age, it is time to focus on securing a larger share of the market.

After introductory adverbs and short phrases indicating time, frequency, location or cause, the comma is omitted unless needed to avoid ambiguity or add emphasis:

  • By next week the new budget will have been thoroughly analysed.

but

  • In 1994, 1457 employees started using the new operating system.

Introductory adverbs or phrases used to mark transition or to express a personal comment are usually set off by commas:

  • Nevertheless, the program will go ahead as scheduled.
  • In short, no hiring is currently taking place.

The introductory phrase may also consist of an adjective or participle separated from its noun by the definite or indefinite article:

  • Unprepared, the team was no match for its opponents.
  • Clearly upset by the heckling, the speaker stopped for a moment to regain his composure.

Conversely, it is sometimes possible to omit the commas that ordinarily set off non-restrictive elements, without obscuring the meaning. This is especially true of short adverbial expressions:

  • Her words went of course unheeded.
  • All the same he had no compunction about slipping the waiter a few dollars to be on the safe side.

In such sentences the addition of commas not strictly needed for clarity gives emphasis to the elements thus enclosed:

  • Her words went, of course, unheeded.

(b) Absolute expressions

One form of non-restrictive expression is the absolute1 construction: a participial phrase grammatically unconnected with the rest of the sentence. Such phrases are followed by a comma:

  • Weather permitting, the conference will be held as planned.
  • The chapter completed, I returned to my former duties.

Note the following errors in the punctuation of absolute expressions:

  • The investigation had been completed, and the results, having been known for some time, the public was anxiously waiting for heads to roll.
    (remove comma after results)
  • We were unable to answer her questions. The truth being that we hadn’t given the matter much thought.
    (replace the period after questions with a comma or dash)

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  • Back to the note1 Do not confuse absolute constructions with those involving dangling or unrelated participles:
  • Listening to his speech, it felt as if he would drone on all day.

This common problem is avoided if the sentence is recast so that the subject of both clauses is the same:

  • Listening to his speech, I had the impression that he would drone on all day.

(c) Parenthetic expressions

Parenthetic expressions are non-restrictive and therefore require commas:

  • We could see that the plan, if not actually rejected out of hand, was far from popular with senior management.

If a parenthetic expression is removed from the sentence, the remainder of the sentence should read as a coherent, grammatically correct whole. For example, the sentence

  • The task force wanted to show that it was as good, if not better, than its predecessors.

is unacceptable because "as good . . . than" is incorrect English. The sentence should be recast as follows:

  • . . . it was as good as, if not better than, its predecessors.

Occasionally it may be expedient to omit the first of the pair of commas around a parenthetic expression:

  • But without realizing it, he had sparked a whole new controversy.

The parenthetic phrase here is "without realizing it."

Both commas can sometimes safely be omitted; under no circumstances, however, should the second comma be omitted while the first is retained:

  • But without realizing it he had sparked a whole new controversy.

not

  • But, without realizing it he had sparked a whole new controversy.

Parenthetic expressions may be set off by parentheses or dashes instead of commas, depending on the degree of emphasis or pause desired, or the length of the expression. Compare:

  • Jane (evidently) had no stake in seeing the dispute continue.
  • Jane evidently had no stake in seeing the dispute continue.
  • Jane, evidently, had no stake in seeing the dispute continue.
  • Jane—evidently—had no stake in seeing the dispute continue.

A common error occurs with parenthetic phrases following the conjunction that. The comma that belongs after the conjunction is often placed before it instead:

  • The odd thing was, that no matter how he tried, he couldn’t remember where he had left the document.

(d) Appositives

Restrictive and non-restrictive appositives should be carefully distinguished. The latter are set off by commas, whereas the former are not:

  • St. John of the Cross
  • Graham St. John, of Hoary Cross
  • Her painting Reflections drew a poor response from the public.
  • Her first painting, Contrasts, has been little studied.

As in the case of parenthetic expressions, the comma following a non-restrictive appositive cannot be omitted. Thus the sentence

  • The statement by the Government House Leader, Herb Gray that no changes would be made to salaries paid to Parliamentarians was not unexpected.

is incorrect. A comma is required after "Gray."

Non-restrictive appositives in final position are usually preceded by a comma:

  • Our supreme governors, the people.

Often, however, the comma is replaced by a colon or dash:

  • Tact: a quality that no skilled diplomat can do without.
  • Margaret Laurence—perhaps the greatest writer to come out of Manitoba.

If the appositive contains internal commas, it is best introduced by a mark other than the comma. In the following example, a colon would be an improvement over the comma after legacy:

  • The Pearson government left behind a remarkable legacy, a pension plan, a universal medicare plan and a new flag.

(e) Annunciatory expressions

The annunciatory expressions namely, that is and for example are usually followed by a comma. They may be preceded by a comma, a dash, a semicolon or a period, or, together with the matter they introduce, may be enclosed in parentheses, depending on the emphasis desired:

  • Plans for Senate reform should be honestly and objectively assessed, that is, bearing in mind only the public good.

The abbreviations i.e. and e.g.—although these are identical in meaning to that is and for example—should be preceded by a comma, a dash or an opening parenthesis, but need not be followed by a comma.

Note that the expression such as is used to introduce an example, not an appositive, and therefore is not followed by a comma. It may be preceded by a comma or other punctuation, as required in the sentence.

(f) Vocative forms

Vocative forms are non-restrictive and are set off by commas:

  • Gentlemen, where I come from, a black-hearted bastard is a term of endearment.
    —Donald Gordon
  • Awake, my country, the hour is great with change!
    —Charles Roberts

Similarly, exclamations and interjections are set off by commas (or exclamation marks):

  • God, what a lot we hear about unhappy marriages, and how little we hear about unhappy sons and daughters.
    —Robertson Davies