Commas, semi-colons and colons

Commas divide sentences into different types of component parts. Commas are generally used to separate grammatical units (words, phrases or clauses) from each other, as the following examples show:

By the great, grey, green, greasy Limpopo river.

On the other hand, when Sherlock Holmes considered the case …. I came, I saw, I conquered.

If you read any or all of these examples aloud, you will immediately notice that, in addition to separating the grammatical elements from each other, the commas also indicate slight pauses. If a slightly stronger pause is needed, a semi-colon would be appropriate. Thus there is a more declama-tory, perhaps even dramatic, tone to:

I came; I saw; I conquered.

There is significant variation of usage of commas where some single words are used to start sentences. For example, in

Originally, punctuation formed no part of written English ….

many highly literate writers would omit the comma after originally, and many commentators would regard both usages as being acceptable. Of course, the point is not limited to originally, but applies equally to all adverbs – such as fortunately, eventually, slowly, and so on – which are often used on their own to begin sentences. (Most English adverbs end in ly, although, as the next example will show, however is a very common exception.) On the other hand, there are apparently similar sentences where the use of a comma would be quite simply wrong by anyone’s standards. For example,

However hard I try to lose weight ….

simply cannot take a comma after however. But the people who would regard it as optional in the previous example would also regard it as being optional in, for example

However, I found that taking more exercise helped me to lose weight.

Since the comma after however will sometimes be essential, sometimes optional and sometimes wrong (depending on the sentence in question), it follows that the interests of both consistency of style and immediate clarity of meaning, will be served by using it where it is optional.

The colon is the strongest pause short of a full stop, with which, in some situations at least, it is practically interchangeable. So, reverting to a previous example, it would be perfectly acceptable to write:

He was handsome: and I do mean handsome.

Indeed, by way of an aside, and as an indication of the incremental nature of these things, once you have seen this sentence written with a colon, you may realise that it could also be written with a semi-colon instead (we have already noted this possibility in the case of the had had example):

He was handsome; and I do mean handsome.

You could even use a comma, although this would lose a significant part of the emphasis which the other versions convey:

He was handsome, and I do mean handsome.

If you try reading all three versions aloud, varying the weight of the pause on an increasing scale of comma, semi-colon, colon, you will see clearly that, in examples such as these, the usage you choose is a question of the effect you wish to achieve, rather than of being right or wrong.

Returning to the potential interchangeability (at least in some situations), of colons and full stops, it is important to sound a note of caution. More particularly, you should not take this potential interchangeability as a licence to join long lists of clauses into very long sentences. As we shall say again in the context of style (see p. 175), there is a useful rule of thumb to the effect that any sentence of more than about 20 words should be scrutinised carefully, to see whether it could not, with benefit, be broken down into two or more sentences.

There are two final points to make about commas. First, they can be used in pairs to divide off a word, phrase or clause which could be removed without affecting the essential meaning of the sentence.

The best writers, however, use punctuation very carefully.

The best writers, but not necessarily run-of-the-mill hacks, use punctuation very carefully.

The best writers, which is a category that unfortunately does not include all students, use punctuation very carefully.

In each case, the main point of the sentence is simply that the best writers use punctuation very carefully.

The third point to be made about commas is, in some ways, a variation on the second; but isolating it into a category of its own is a useful way of emphasising its importance. Consider the following sentence:

Essays which must be sent to the external examiner must be in a form suitable for photocopying.

This could bear either of two meanings. First, inserting two commas gives:

Essays, which must be sent to the external examiner, must be in a form suitable for photocopying.

In other words, all essays have to be sent to the external examiner and they all have to be in a form which is suitable for photocopying. If this is what is meant, it should be rewritten as:

Essays must be sent to the external examiner and must be in a form which is suitable for photocopying.

The second possibility is:

Essays which must be sent to the external examiner, must be in a form which is suitable for photocopying.

In this case, inserting a single comma has changed the meaning so that it is only those essays which have to be sent to the external examiner which have to be in a form which is suitable for photocopying.

If this is what is meant, it should be rewritten as:

If an essay must be sent to the external examiner, it must be in a form which is suitable for photocopying.