Take a breath: use a comma

The comma is such a neat little invention. Its purpose is to signal a break between groups of words in a sentence. This helps make the meaning clear, and gives the sentence a conversational flow. 

We use commas far less now, and generally this doesn’t alter the meaning.
      With commas: After his divorce, he moved to Singapore, but returned every year.  
      Without commas: After his divorce he moved to Singapore but returned every year.

But sometimes, leaving out these natural pauses can get you into trouble. 

Before –ing words  

One common pitfall lurks in a particular sentence structure that uses an –ing phrase (known as a present participle), such as working, showing, running. Without a comma, the effect is of a breathless, non-stop statement. If you were speaking, you would pause. And what’s worse, without a comma the meaning is often unclear.

Here’s an example: 

He regretted his decision stating he would never use the drug again. 
Was his decision never to use the drug? No! It was to use the drug. 

Here’s how a comma clarifies the meaning: 
He regretted his decision, stating he would never use the drug again.

Another example:

On her second attempt she rebounded with vigour clearing the bar easily. 

You have to read this twice to get the meaning. A comma in the right place solves the problem:

          On her second attempt she rebounded with vigour, clearing the bar easily.

And how about this:

The researchers want to find out where toxins originate and end up using hydrodynamic modelling.

This is confusing. It sounds as if the researchers ‘end up using’ the modelling. Once again, the comma makes it clear:

The researchers want to find out where toxins originate and end up, using hydrodynamic modelling.

Say it aloud

So how do you know whether to add a comma? The trick is to sound out the sentence. Did you say it without any pauses? Or did you naturally make a break before the –ing word: clearing, saying, using? If so, you need a comma!