Commas 3

Commas are commonly used before a joining word when linking two complete independent (or dominant) sentences. A complete sentence is one that can exist by itself and makes complete sense (... it has its own subject and its own verb). A joining word (conjunction) are words such as and, but, although, or, when and if.

If either of the two phrases within a sentence is not complete (for example it doesn't have its own subject or verb), then no comma is used before the joining word. Look at the examples below to see this demonstrated.

I knew the opposition were good, but I had never seen them play.

I knew the opposition were good but had never seen them play.

You have to be a little careful with this advice. A comma can be ommitted before conjunctions joining two short complete sentences (see example below) ...

I walked to town, but Mary cycled.

A comma separates a dependent clause from an independent clause.

In order to save New Zealand from bankruptcy, the government is selling its assets at discount prices.

This is fun! Watch the BBC's video and try their three games on compound sentences: BBC lesson on connectives. (Not iPad friendly).