Above I claimed that I was not allowed to join two sentences with a comma. This is true, but not quite. A comma can be used to join two complete sentences into one single sentence but only under the condition that it is followed by a connecting word. These connecting words are – you might have guessed it – the famous ‘fanboys’: for, and, nor, but, or, yet, so.

As a German student, I sometimes tend to put a comma without adding one of the fanboys. This tendency is due to the existence of a German rule of a serial comma between two main clauses.

How can we solve this problem?
If I think the sentences are closely connected, I just put a semi-colon between them. Either we must have the comma followed by one of the fanboys, or we must replace the comma with a semi-colon or even a full stop. As this needs some practice, I have provided an exercise for you.

Exercise: joining two sentences with a comma

State which sentence is correctly punctuated and reflect on the comment.