COMMAS: SOME COMMON PROBLEMS
Imagine a world without commas. You may think that these small marks are nearly irrelevant, but what happens when you try to read the following passage from an essay by Oliver Sacks quickly? We’ve omitted most commas:
(1) Dr. P. was a musician of distinction well-known for many years as a singer and then at the local School of Music as a teacher. (2) It was here in relation to his students that certain strange problems were first observed. (3) Sometimes a student would present himself and Dr. P. would not recognize him or specifically would not recognize his face. (4) The moment the student spoke he would be recognized by his voice. (5) Such incidents multiplied causing embarrassment perplexity fear and sometimes comedy. (6) For not only did Dr. P. increasingly fail to see faces but he saw faces when there were no faces to see. . . (7) [W]hen in the street he might pat the heads of water hydrants and parking meters taking these to be the heads of children, he would amiably address carved knobs on furniture and be astounded when they did not reply (The Man Who Mistook His Wife for a Hat).
As you can see, reading without commas slows you down. Reading unpunctuated prose—or worse, incorrectly punctuated prose—is like trying to listen to a news report on a radio with poor reception; static gets in the way of basic understanding, and it is easier to tune out than try to decipher the meaning from the bits and pieces of information that come through. Now, perhaps, you have a better idea why professors and preceptors see commas as such a significant part of good writing. If your paper is filled with static because it is incorrectly punctuated, it can be difficult, even impossible, for your readers to follow your argument. Punctuation marks, such as commas, indicate the grammatical and logical structure of your ideas, emphasize important words or phrases, and mark the rhythm of your sentences.
Poor Grammar Can Indicate Weak Ideas
Before you begin to wrestle with the rules and conventions regarding commas, you should be aware that many writers make mistakes or awkward choices in how they punctuate sentences simply because their ideas are not clear in their own minds. If you are having trouble phrasing a sentence coherently, check to see that your ideas are coherent first. Then, as you write, keep your reader in mind and make an effort to construct your sentences as clearly as possible. In addition, you can often make decisions about where you need commas if you read your work out loud and place commas where you naturally inject pauses.
Commas Joining Independent Clauses
An independent clause is a group of words containing a subject and verb that can stand alone as a sentence, such as “A student presented himself” and “Dr. P. did not recognize him.” When such clauses are joined by coordinating conjunctions—words such as and, but, for, or, nor, either...or, neither...nor, both....and, not only...but, etc.—they are generally (but not always) punctuated with a comma immediately before the conjunction. For example, sentence 6 above should contain a comma before the conjunction: “For not only did Dr. P. increasingly fail to see faces, but he saw faces when there were no faces to see. . . .”
When two independent clauses are adjacent and joined by a comma, but not by a coordinating conjunction, this is generally considered a grammatical error, variously called a run-on sentence, a comma splice, or a comma link. See example 7 above. This mistake can be corrected in numerous ways: by adding a conjunction; by punctuating the clauses as separate sentences; or by using a semi-colon rather than a comma between the clauses. Sacks punctuated it as follows: “[W]hen in the street he might pat the heads of water hydrants and parking meters, taking these to be the heads of children; he would amiably address carved knobs on the furniture and be astounded when they did not reply.” For stylistic reasons, writers sometimes choose to join two short, simple, clearly related sentences with a comma. Carefully consider your professor’s or preceptor’s opinions about grammar before doing so in an academic essay. For students, it is often better to be adventurous with ideas and conservative with grammar.
Commas with Adjectival Phrases, or Clauses
Some phrases function descriptively as adjectives, modifying a noun. Some such phrases are restrictive; they are essential to the meaning of the noun they modify. These phrases do not need to be set off by commas. Non-restrictive phrases—phrases that are not essential to the meaning of the noun they modify—should be followed, set off, or preceded by commas. See for example, sentence 1 above. The phrase “well-known for many years as a singer” further describes what kind of distinguished musician Dr. P. is, though it is not essential to the meaning of the sentence. Sacks, therefore, sets the phrase off with commas: “Dr. P. was a musician of distinction, well-known for many years as a singer, and then, at the local School of Music, as a teacher.”
Another common type of phrase that must be separated from the rest of the sentence by commas is the non-restrictive participial phrase. In sentence 5, Sacks uses a non-essential participial phrase to modify the noun “incidents”: “Such incidents multiplied, causing embarrassment, perplexity, fear—and sometimes, comedy.” (Note also that in this sentence Sacks places commas between items in a list and employs a dash to emphasize the pause before the last item, comedy.) Another example of a non-restrictive participial phrase exists in sentence 7: “[W]hen in the street he might pat the heads of water hydrants and parking meters, taking these to be the heads of children. . . .”
Non-restrictive adjectival clauses are also set off by commas, such as in the sentence: Dr. P. amiably greeted phantom faces, which appeared to him in water hydrants and parking meters.
Commas with Adverbs and Adverbial Phrases and Clauses
Some words, phrases, and clauses function as adverbs, modifying a verb, adjective, or another adverb. Generally, you do not need to punctuate single adverbs unless they are in an unusual position, such as at the very beginning or very end of a sentence. In sentence 3 above, for example, Sacks needs to set off the word specifically in order to clarify his meaning: “. . . Dr. P. would not recognize him; or, specifically, would not recognize his face.” There are a few common adverbs—however and therefore, for example—that are usually set off with commas, no matter what position they take in a sentence.
When prepositional phrases begin sentences, they are often, but not always, followed by a comma. (How’s that for an ambiguous rule?) Make your judgment based on the conventions regarding specific phrases and on whether punctuation will help to clarify your meaning or mark the rhythm of the sentence. [Idiomatic phrases, such as for example and of course, are (almost) always set off by commas.] When a prepositional phrase falls within a sentence, whether you punctuate it depends entirely on how you use the phrase, where it is placed, what rhythm you want to create, and, most important, whether the phrase interrupts the normal grammatical flow of the sentence. For example, see sentence 2 above, where Sacks must set off the phrase that begins with in relation because it interrupts the sentence: “It was here, in relation to his students, that certain strange problems were first observed.”
When adverbial clauses (such as this one) precede the main clause, a comma is placed between them. Writers sometimes choose to omit the comma if the initial clause is short. In sentence 7 above, for example, Sacks writes: “[W]hen in the street he might pat the heads of water hydrants. . . .”
In sentence 4, however, the introductory clause is longer, so the sentence is clearer when there is a comma before the main clause: “The moment the student spoke, he would be recognised by his voice.” As with adverbial phrases, adverbial clauses that interrupt the grammar of a sentence are usually set off with commas. When such clauses fall in the closing position, whether you choose to punctuate will depend upon issues of clarity and rhythm.
Commas with Appositives
An appositive is a word, phrase, or clause which is interjected to identify or explain another word or words in the sentence: an appositive, a difficult term to describe, is generally easy to recognize. Some appositives are restrictive or essential; they are needed to define the noun to which they are appended. Essential appositives are not set off by commas, such as in the sentence: an appositive that is essential to defining its subject is not set off by commas. Many appositives, however, are non-restrictive. They are not essential to the meaning of the sentence and must be preceded or set off by commas. The following sentence uses such an appositive: Oliver Sacks, writer and neurologist, does not use any appositive phrases in the paragraph quoted throughout this handout.
Sources for More Detailed Information
This handout could not possibly provide a complete list of rules regarding commas. (Any attempt would be extraordinarily dull, exceedingly long, and, finally, incomplete.) If you need basic information on how to use commas or have very complex and specific questions, you should refer to a manual of editorial style and usage or to a grammar handbook. You may take a look at any of these reference books which are available in the Writing Center’s library.
Please note: if you are having difficulty with commas, it is best not to rely entirely on a computer grammar program to find your mistakes. Because the variable rules and conventions regarding commas cannot be reduced to a set of prescriptions, computer grammar programs tend to recommend only simple syntax and punctuation solutions.
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