Using the Comma in Formal English Prose
The comma is used in English prose in a wide variety of ways. Personal preferences, document content and reader needs are often concerns when making decisions about comma placement, but so too are publisher guidelines and punctuation rules. There are basic patterns of comma use that are considered correct and appropriate for the kind of formal prose expected of academics, scientists and professionals. Fortunately, these patterns also enable the construction of complex and interesting sentences with greater variation in sentence structure, so they are well worth learning and putting to good use.
• A comma is generally used after an introductory clause, phrase or word that opens a sentence and sets the stage for what follows. The introductory material may form a dependent clause or perhaps a participial, infinitive or prepositional phrase, or it may simply be a single adverb. ‘When we heard the weather forecast, we decided to move the trial indoors’ and ‘To reproduce the outdoor conditions, we adjusted the lighting at intervals throughout the day’ demonstrate correct use of the comma after an introductory clause in the first instance and after an introductory phrase in the second. In many cases short introductory phrases (the first three words of this sentence being a good example) do not require a comma, but adverbs such as ‘however’ do when they stand alone in an introductory position. In ‘However, we failed’ a comma should therefore follow ‘however’ immediately, but in ‘However hard we tried, we failed’ the comma should come after the entire introductory phrase.
• A comma is often used to separate independent clauses that are joined by a coordinating conjunction, so ‘I completed my research that morning, but she received good news from the publisher in the afternoon’ uses a comma before the conjunction ‘but.’ The comma is not always necessary, so if the clauses are short or share a subject, the comma is often eliminated, as it is in ‘I completed the first trial and moved on to the second.’ The clarity of each sentence should be the main concern when deciding upon comma use in these situations, but consistent punctuation patterns are also important and may help when making decisions for tricky cases.
• Commas are used to enclose and thus separate or highlight words, phrases or clauses that appear in the middle of a sentence but are not essential to the main meaning of the sentence. Words are nonessential to a sentence if the sentence still makes sense when they are removed. Examples include ‘The second day, when the worst of the weather hit, was the only day we could use the park’ and ‘The professor, frowning in a most unpleasant way, looked up from my essay.’ In each case the clause within commas modifies the action in important ways, but the rest of the sentence would function effectively, though it would certainly be less interesting and informative, were that extra material removed.
• Commas are also used to separate three or more words, phrases or clauses that are written in a series within a single sentence. ‘I arranged the laboratory, the participants, the equipment and the assistants’ and ‘The objective was to devise methods for exploring the problem, to use the results achieved through those new methods to design the most effective solutions, and to provide those who are suffering with a safer environment.’ The final comma in the second example – the one that appears before the conjunction ‘and’ – is known as the serial or Oxford comma and is not strictly necessary, so you may or may not want to use it. Some publisher guidelines will state a preference either way, and consistent patterns of usage should be maintained throughout a document, but even when the serial comma is not normally used in a text it can be employed to clarify the meaning and structure of a sentence when the individual items in a series are long, complex and already contain punctuation.
