Page 121 - How to write effective business English your guide to excellent professional communication by Fiona Talbot

110 How to Write Effective Business English

In order to use commas correctly, it helps to know that a comma
signifies a brief pause. Very often, people wrongly use a comma to
do the work of a full stop (period). For example:
I examined the computer, it had obviously been damaged.

As there are two complete statements here, not just a pause, we
could try a full stop: ‘I examined the computer. It had obviously
been damaged.’ However, this sounds rather stilted and a native
English writer is likely to use a conjunction to add fluidity. For
example: ‘I examined the computer and found it had obviously
been damaged.’
A comma is also used to link lists of items, groups of words,
adjectives, actions and adverbs. For example:

She listed, there and then, the things she would need for
her presentation: a laptop, a projector, screen, flipchart and
marker pens.

Apostrophes show where one or more letters have been left out of
a word. For example:
I’m = contraction of ‘I am’;
It’s = contraction of ‘it is’ or ‘it has’;

You’ll = contraction of ‘you will’.
Apostrophes can also show possession or ownership. For example:

The student’s rights = the rights of one student;
The students’ rights = the rights of students.

The general rule is:
apostrophe before the s (’s ) = singular possession;

apostrophe after the s (s’) = plural possession.
Unfortunately, English always has some irregular forms, such as:

men = plural of man; but the possessive is men’s;
children = plural of child; but the possessive is children’s;
its = possessive of it – yet takes no apostrophe at all!