This is actually very easy, but people often get it wrong.

Most people whack in a comma at the end of all opening clauses that contain a verb. In Australia, at least, this is not the right way to go about things. Sometimes such clauses take a comma; sometimes they don’t.

If you’re Australian and you want your editing to be above reproach, read on. It isn’t hard to get your head around. There’s actually a simple rule you can follow. It is:

Clauses introduced by as. since and while that express time, don’t take a comma. When these same clauses express a cause, they do.

For example:

While he was waiting for her to get ready he drank three martinis. (Time)

While you might think otherwise, I’m convinced I’m right. (Cause)

As he was thinking these thoughts a butterfly flew past the window. (Time)

As you no longer wish to go to the moves with me, I will go alone. (Cause)

Since World War One ended society hasn’t been the same. (Time)

Since you no longer wish to be president, I nominate Susan. (Cause)

There’s only one thing you need to watch out for. Sometimes clauses introduced by as, since or while and involving time can be confusing if a comma isn’t used.

For example:

Since the new boss took over the place hasn’t been the same. (Time)

If you follow the rule slavishly, you won’t use a comma. But without a comma the reader tends to read: Since the new boss took over the place … Round about now they realise the sense is meant to be different from this, and they have to backtrack. To avoid readers backtracking (never a good thing), break the rule and use a comma.

Since the new boss took over, the place hasn’t been the same.

And that’s all there is to it.

Except:

Sometimes when is used in the same way as while. For example:

When we were walking in the forest we saw two foxes.

On occasions where when is used in a clause to convey time, the same rules apply.

And there you have it.

Simples.