avoid sentence errors
There are two types of sentence error:
1   Writing an incomplete sentence, i.e. one that does not contain a subject
    or a finite verb, or does not express a complete idea.
2   Writing two or more sentences with only a comma between them.
The most common error of sentence structure is joining two or more sentences
together with only a comma between them. People seem to do this less often
when the subjects of the sentences are different than when they are the
same. Fewer people would write:
•  The client ran down the road, the supervisor ate a doughnut.
than
•  He ran down the road, he was in a hurry.
A moment’s thought will show that the structure of both these ‘sentences’ is
identical and, if one is wrong, both are wrong.
1   The client  ran  down the road,
2   The supervisor ate a doughnut.
3   He ran down the road.
4   He was in a hurry.
These mistakes happen because the writer feels that the sentences are too
short and that, as they belong together in meaning, they ought to be joined.
This may be true, but using a comma is not the way to do it.
Let us look again at the faulty construction:
    •  He ran down the road, he was in a hurry.
There are four ways of putting this right:
1   He ran down the road.  He was in a hurry.
2   He ran down the road; he was in a hurry.
3   He ran down the road because he was in a hurry.
4   Being in a hurry, he ran down the road.