Commas

The comma is a useful device that can make your text more reader friendly. It is typically used to separate words in a list:

The study includes grammar, semantics and phonetics.

Note in the above example, there was no comma before ‘and’. This means that it could be interpreted in two ways:

. . . [grammar], [semantics], and [phonetics]

or . . . [grammar], [semantics and phonetics]

If you want to make more explicit that there are three separate items in the list, you can use the so-called Oxford comma before and to disambiguate:

The study included grammar, semantics, and phonetics.

Commas can also be used to separate extra information, typically at the beginning of a sentence:

Among the 20 countries included in our analysis, we estimate . . .

During the past 20 years, the incidence has increased by 20%.

Commas: main clause and subordinate clause

Commas are also used to separate a main clause from a subordinate clause. A main clause is an independent clause typically comprising a subject and a verb which can stand on its own. A subordinate clause (italics) is dependent on a main clause and cannot stand on its own.

Since the results of this study are inconclusive, a decision was made to . . .

After careful analysis of the data, we conclude that . . .

Subordinate clauses often start with a subordinating conjunction such as, because, while, since, after etc.

Commas: relative clause

There is also a type of subordinate clause known as a relative clause. Commas should not be used in restrictive relative clauses:

1a) This is the approach that/which was used to calculate the percentage.

In example 1a), the noun ‘approach’ is being defined by the relative clause and therefore there is no comma. Note that you have a choice between that and which in such cases. The grammar check on your computer may suggest that you use that but both are grammatically correct. In contrast, in a non-restrictive relative clause, the clause is simply adding extra information and commas are present:

1b) The book, which was published in Oxford, has been a great success.

Here, the sentence is The book has been a great success and the non-restrictive relative clause simply adds extra information about it being published in Oxford.

Colons (:)

Colons may be used to introduce a list of items:

These are the options available: to discontinue or to elaborate.

It can be used before a clause or phrase that adds more information to the main clause:

This aspect has been neglected for some time: it was thought to be obsolete.

(N.B. a semi-colon or full stop would also be possible here)

Semi-colons (;)

A semi-colon may be used instead of a full stop to join two sentences that are closely linked:

The study included a wide range of grammatical features; this scope entailed an impressive collection of results.

Hyphens

A hyphen is used to join two pre-modifying words before a noun as in:

A fifty-page article

Three-lane motorways

As an example of language change, it is also found in other compounds illustrating the development of two separate words into a compound. There are no fixed rules concerning when a word is hyphenated or changed into a compound, so it is worth checking the literature in your field to see which form of the word is used:

black board, black-board, blackboard
COVID-19 or COVID19
Sub-clause or subclause
Second-hand or secondhand