The joining comma

The joining comma is used to join two complete sentences into a single sentence.

It must be followed by one of the following conjunctions: and, but, or, so, while, yet.

Have a look at this example:

The operator of the vehicle is liable for any damage caused by the vehicle’s operation, and such liability cannot be avoided.

It also works as two sentences:

The operator of the vehicle is liable for any damage caused by the vehicle’s operation. Such liability cannot be avoided.

When you join two sentences with a comma and a conjunction you create a “compound sentence”.

More examples:

The Employee is entitled to a mobile phone to use for work-related purposes, and the cost of work-related phone calls is covered by the Employer.

We would be glad to offer you our services, but we must first ensure that there will be no conflict of interest.

You must submit the application and supporting documentation by 31 December, or you will have to start the entire procedure again.

Unfortunately we failed to meet the deadline, so we will have to submit the application again.

Sales tax is collected only at the point of final sale to the customer, while VAT is collected at different stages of the production process.

Remember that you must use a conjunction with a joining comma. It is incorrect if you use a comma without a conjunction:

Sales tax is collected only at the point of final sale to the customer, VAT is collected at different stages of the production process.

This mistake is very common. It’s called a “comma splice”.

It can be correct, however, to use a semicolon in place of a comma in such sentences:

Sales tax is collected only at the point of final sale to the customer; VAT is collected at different stages of the production process.

Note that you cannot use words like therefore, however, nevertheless, thus, consequently, meanwhile or hence as connecting words after a joining comma. They require a semicolon:

Unfortunately we failed to meet the deadline; therefore we will have to submit the application again.

We accept that this issue will cause a delay; however, we see no reason to cancel the project.

The contract was not signed by an authorised representative; consequently you should not proceed with the transaction until you have received a correct signature.