Written by Jerry Plotnick, University College Writing Centre

Many students do not take full advantage of punctuation. They never venture beyond the comma and the period—the two punctuation marks that nobody can do without. Some are afraid that if they use other forms of punctuation, they will do so incorrectly, so they never take the risk. Learning to punctuate effectively does involve learning the rules, and this handout summarizes the most important of them. But learning to punctuate is about much more than rules. Punctuation, when skillfully deployed, provides you with considerable control over meaning and tone. Try to experiment with all forms of punctuation in order to expand your expressive range as a writer. And observe closely how accomplished writers use punctuation to good effect. This handout limits itself to punctuation that occurs within sentences: commas, semicolons, colons, dashes, and parentheses.


Commas are the most frequently used form of punctuation and probably the hardest to master. Using commas well is a science and an art: though there are well-defined rules, there is plenty of room to manouevre as well. Both the science and the art of comma use have changed with time. Eighteenth- and nineteenth-century writers, for example, used commas unsparingly. But do not think that comma problems boil down to whether we use too many commas or too few. It is best to learn the rules—and to know which ones can be broken and when. You should break the rules for a purpose and consciously. Intuition is not always the best guide. In particular, the sometimes serviceable practice of choosing a comma whenever you would pause in speech can get you into trouble, especially if you write long sentences and lose your breath easily. Here are a few basic rules to guide you in your comma use:

  1. Commas after many introductory phrases are optional. When the introductory phrase is short, you can often omit the comma; when the phrase is longer, a comma will help your reader recognize where the main clause begins:

    In the early 1960s Murray Gell-Mann and George Zweig independently tried to reduce the tremendous complexity of the zoo of particles then known at the time. (Steven Weinberg, Dreams of a Final Theory)

    After much preliminary speculation and a few unsuccessful hypotheses, he achieved his central insight while reading an apparently unrelated work for recreation. (Stephen Jay Gould, Ever Since Darwin)

    When the introductory phrase includes a participle (a verb form ending in –ing or –ed), always add a comma:

    Sitting in traffic, a plumber can’t plumb and a deliveryman can’t deliver. (Elizabeth Kolbert, “Don’t Drive, He Said”)

    Make sure also to add a comma after an introductory clause (any grammatical unit that contains a subject and a verb):

    As the train straightened after a long curving tunnel near Lhasa, a nomad emerged from his tent on a hillside. (Pankaj Mishra, “The Train to Tibet”)

  2. When joining two independent clauses (clauses that could stand alone as sentences) with a coordinating conjunction (and, or, nor, but, yet, for, so), you normally place a comma before the conjunction:

    Sweetness is a desire that starts on the tongue with the sense of taste, but it doesn’t end there. (Michael Pollan, The Botany of Desire)

    This rule can occasionally be broken. The shorter the two independent clauses are, the more appropriate it is to break the rule. Examples are more likely to be found in fictional prose where the style is deliberately terse:

    It was very hot and the express from Barcelona would come in forty minutes. (Ernest Hemingway, “Hills Like White Elephants”)

  3. When joining mere phrases, you usually do not provide a comma:

    There have been great civilizations in which the peculiar balance of mind required for science has only fitfully appeared and has produced the feeblest results. (Alfred North Whitehead, Science and the Modern World.)

    In this example, the conjunction and joins two verb phrases.

    This rule is frequently broken, particularly when the writer wants to convey surprise or to add an afterthought:

    Each of our internal organs has a personality of its own, and a mythology too. (Sherwin Nuland, The Mysteries Within)

    We cannot remain absolutely free, and must give up some of our liberty to preserve the rest. (Isaiah Berlin, “Two Concepts of Liberty”)

    Just make sure that whenever you break the rule, you do so for a reason.

  4. Place commas between each element of a list of three or more parallel words, phrases, or clauses. Writers often place a comma before the conjunction (and or or) preceding the last element in the list:

    The history of interactions among disparate people is what shaped the modern world through conquest, epidemics, and genocide. (Jared Diamond, Guns, Germs, and Steel)

    Some writers, however, choose not to place a comma before the last element:

    The material consequences in the East of the German occupation, the Soviet advance and the partisan struggles were thus of an altogether different order from the experience of war in the West. (Tony Judt, Postwar)

    Though either method of punctuating is acceptable, try to choose one method and stick with it. A comma before the final element is less likely to produce unintended ambiguity.

  5. Surround interrupting or parenthetical clauses or phrases with commas. Such clauses or phrases are not essential to the sentence. If you removed them, the central point of the sentence would remain:

    Dr. Johnson’s Lives of the Poets, as Boswell tells us, was written at the urging of the London booksellers. (Leon Edel, Writing Lives)

    Richard Lester, the director of Petulia, is a shrill scold in Mod clothes. (Pauline Kael, Going Steady)

    Remember to add commas on both sides of an interrupting phrase or clause: don’t forget the second comma.

    The interrupting element in the last example is an appositive. It restates the meaning of the noun phrase it follows. An appositive can, however, narrow down rather than simply restate the meaning of a noun or noun phrase. When an appositive restates meaning, surround it with commas; when it narrows down meaning, do not:

    Hillary Clinton’s daughter, Chelsea, has been called the Greta Garbo of presidential children because she shuns the limelight. (CBS News Report)

    Charlotte Brontë’s sister Emily used weather to great effect in her novel Wuthering Heights. (Karen Odden, Introduction to Hard Times)

    Hillary Clinton has only one daughter; Charlotte Brontë had more than one sister. Chelsea is therefore not essential to the sentence, while Emily is.

    Another type of interrupting element, the relative clause, also deserves close attention. Relative clauses begin with words such as who, which, that, and sometimes where and when:

    During the past thirty years the ideal of the unity of learning, which the Renaissance and Enlightenment bequeathed to us, has been largely abandoned. (E.O. Wilson, Consilience)

    As with other interrupting sentence elements, the surrounding commas indicate that the information in the clause is not essential to the main point of the sentence. E.O. Wilson is suggesting that there is only one ideal of the unity of knowledge, and we happen to have inherited that ideal from the Renaissance and the Enlightenment. Take the relative clause away, and Wilson’s point remains the same: most intellectuals have abandoned this ideal.

    Some relative clauses, however, are integral to the meaning of a sentence. In such cases, it is critical not to surround the clause by commas:

    The names of the creative writers who have been more or less Freudian in tone or assumption would of course be legion. (Lionel Trilling, “Freud and Literature”)

    In this sentence Trilling makes his assertion not about all creative writers but only about those who are Freudian in their outlook. Remove the clause, and you destroy the sentence’s meaning

    One final, purely stylistic point: for relative clauses that do not take commas, the word which or who can be replaced by that:

    Research that once required days in the stacks or periodical rooms of libraries can now be done in minutes. (Nicholas Carr, “Is Google Making Us Stupid.”)


The semicolon has two main uses. The first is to combine two closely related independent clauses into one sentence:

A scientific genius is not a person who does what no one else can do; he or she is someone who does what it takes many others to do. (Malcolm Gladwell, “In the Air”)

Van Gogh painted almost exclusively from life; Gauguin favored imagination. (Peter Schjeldahl, “Different Strokes”)

In either case, the writer could just as well have used two separate sentences, but using the semicolon helps convey the close connection between two sequential ideas.

The other valid use of semicolons is to separate list elements that are long or complex. If, in particular, those list elements contain internal commas, semicolons will help show just where each element begins and ends:

The Idea of North offers little hard data about the history, geography, population, sociology, politics, or economy of the North; about the burgeoning interest in the North after the Second World War, especially after the creation of the federal Department of Northern Affairs and Natural Resources in 1953; about the aboriginal-land-claims issues being thrashed out in the late sixties. (Kevin Bazzana, Wondrous Strange: The Life and Art of Glenn Gould)


Colons offer a way of urging your reader forward. The words preceding the colon create an expectation; the words following the colon fulfill it:

The entomologists’ dream of the built-in insecticide was born when workers in the field of applied entomology realized they could take a hint from nature: they found that wheat growing in soil containing sodium selenate was immune to attack by aphids or spider mites. (Rachel Carson, Silent Spring)

Our age has produced a new literary breed: the self-hating essayist. (Cristina Nehring, “Our Essays, Ourselves”)

The part of the sentence following the colon can expand on an idea (that nature suggests how to take advantage of built-in insecticides) or answer an implied question (who exactly belongs to this new literary breed?). Note that a colon is generally preceded by a full independent clause. It can, however, be followed either by another independent clause, a phrase, or even a word. The phrase sometimes takes the form of a list:

Shakespeare’s archvillain had many Shakespearean forerunners: the melodramatic Richard II, the casuistical Pandulph, the sly and crafty Ulysses. (Harold C. Goddard, The Meaning of Shakespeare)


Dashes serve some of the same functions as commas and colons, but they assert themselves more forcefully. Like commas, dashes are used to set off interrupting clauses or phrases, but a pair of dashes will tend to call more attention to what lies in between:

Old Beijing—designed for pedestrians and imperial processions but not much in between—has turned out to be a bad framework on which to construct a modern city. (Paul Goldberger, “Forbidden Cities”)

Acting alone, a dash, like a colon, allows you to expand on or to complete an idea, and dashes used this way are often interchangeable with colons. But the dash tends to be a little more abrupt and is particularly good at suggesting irony or surprise:

Nobody ever recommended or even suggested that I be a novelist—in fact, some tried to stop me. (Haruki Murakami, “The Running Novelist”)

The dash has one other occasional use. Following a list, a dash allows you to tie things together with an explanatory independent clause:

The manner of giving, the thing which is given, the effect of the giving upon the individual—these are the factors which determine the progress of the Sufi. (Idries Shah, The Sufis)

If you don’t use dashes, adding them to your repertoire will considerably broaden your expressive range as a writer. But be careful: overusing them will blunt their overall impact.


Parentheses offer a third way of introducing interrupting material. A pair of commas supplies the standard, matter-of-fact way of doing so. If dashes provide a more forceful alternative to commas, parentheses offer a tentative and modest one:

Paul, like Jesus, encouraged celibacy not because he loathed the flesh (which in my opinion he did not) but out of his urgent concern for the practical work of proclaiming the gospel. (Elaine Pagels, Adam, Eve, and the Serpent)

A parenthetical aside often sounds like a footnote. It need not always be perfectly integrated into the sentence:

In one sense, the “epistemic” sense (“epistemic” here means having to do with knowledge), science is indeed objective. (John R. Searle, Consciousness and Language)

Parentheses can also enclose full sentences. The period goes inside the closing parenthesis:

Ondaatje was born in 1943, into a prominent Sri Lankan family. (He has written a memoir of his relatives, Running in the Family, published in 1982.) (Louis Menand, “The Aesthete”)