Punctuation: comma

The basic sentence

We do not use commas to separate the basic parts of a sentence (subject and verb, verb and object).

• The standard of living of the dock workers was slowly improving. (not The standard of living of the dock workers, was slowly improving.)
• Many of them were able to begin buying their own homes. (not Many of them were able to begin buying, their own homes.)

Before and after the basic sentence

If we put long adverbial expressions before the basic sentence, we often use a comma. Compare:

• At that time the standard of living of the dock workers was slowly improving.
• During the late 1920s and early 1930s, the standard of living of the dock workers was slowly improving.

We do not so often put commas when adverbial expressions come after the basic sentence.

• The standard of living of the dock workers was slowly improving during the late 1920s and early 1930s.

Inside the basic sentence

When adverbial expressions come between or inside parts of the basic sentence, we may put commas before and after them.

• The standard of living of the dock workers, during the late 1920s and early 1930s, was steadily improving.

Noun phrases

We do not usually separate a noun from the adjectives or other expressions that go with it.

• the mainly foreign labourers (not the mainly foreign, labourers)
• the mainly foreign labourers in the north-eastern docks (not the mainly foreign labourers, in the north-eastern docks)

However, we do use commas to separate non-identifying expressions (see here).

• Andreas Bergmeister, who established the dock workers’ union, …

Sentences with conjunctions

We often put commas in sentences with conjunctions, especially in longer sentences. Compare:

• The situation changed when the export markets began to contract.
• The situation changed noticeably for the worse after 1932, when the export markets began to contract.

We usually use a comma if we start with the conjunction.

• When the export markets began to contract, the situation changed.

Indirect speech

We do not put commas after verbs of saying, thinking, etc in indirect speech.

• Many commentators declared that the economy was in serious trouble. (not Many commentators declared, that the economy …)
• No one knew how serious the situation would become. (not No one knew, how serious …)

A useful rule: we do not put a comma before that (conjunction or relative pronoun).

• They did not understand that the economic conditions that had existed earlier had disappeared for good.

Between grammatically separate sentences

Between grammatically separate sentences (with no conjunction), we use a full stop or a semi-colon, but not a comma. Compare:

• Orders began to dry up, and most companies reduced their work force. (comma and conjunction)
• Orders began to dry up. Most companies started to reduce their work force. or Orders began to dry up; most companies started to reduce their work force. (but not Orders began to dry up, most companies started …)

Conjunctions and adverbs

Note that some linking words (e.g. consequently, however, therefore) are adverbs, not conjunctions. A sentence beginning with an adverb is grammatically separate from the sentence before it; consequently, a full stop or semi-colon is necessary between the sentences (see here).

• Orders began to dry up. Consequently, most companies started to reduce their work force. (not Orders began to dry up, consequently, most companies …)
• Orders began to dry up; however, some companies tried to carry on as before. (not Orders began to dry up, however, some companies …)

Commas between adjectives

Before a noun, we use commas mostly to separate adjectives that give the same or related kinds of information.

• a tall, impressive figure
• a long, boring speech
• an expensive, ill-planned, wasteful project

Commas are sometimes dropped between short adjectives.

• a tall(,) dark(,) handsome cowboy

Commas are not dropped when adjectives or other modifiers refer to different parts of something.

• a green, red and gold carpet (not a green red and gold carpet)
• concrete, glass and plastic buildings

Before a noun, commas are not normally used when adjectives give different kinds of information.

• Have you met our handsome new financial director? (not … our handsome, new, financial director)
• surprising new developments
• gloomy economic forecasts

After be and other linking verbs, adjectives are punctuated like a list (see below).

• His speech was long, boring, detailed and irrelevant.
• The cowboy was tall, dark and handsome.

Lists

We use commas to separate the different things in a list (but not usually before and unless the last item is long). Compare:

• The developing crisis affected manufacturers, distributors, marketing organisations, banks and credit agencies.
• … marketing organisations, banks, and some of the major credit agencies.

Numbers

Commas are used to divide large numbers into groups of three figures, by separating off the thousands and millions.

• 6,435 (not 6.435)
• 7,456,189

We do not always use commas in four-figure numbers, and they are never used in dates.

• 3,164 or 3164
• the year 1946

Spaces are sometimes used instead of commas.

• There are 1 000 millimetres in 1 metre.

We do not use commas in decimals (see here).

• 3.5 = three point five or three and a half (not three comma five)