Hi Steve. This is one of the more common issues, in my experience. I've done quite a bit of looking into it, 'cos it's one of those issues that clients like to pick up on.
Here's the low-down:
• Commas should be used with a conjunction (and, if, but, etc.) to join two main (independent) clauses. A main clause is one that could stand alone as a sentence... e.g. "I thought it would be long, and it was."
• A comma should not be used with a conjunction to join a main clause with a dependent clause... e.g.: "The cat sat on the window-sill, and occasionally glared at passers-by." THIS IS WRONG - do not use a comma in this instance.
• If, however, these rules cause problems, make an exception... e.g. "The second variable tag (sTag2) replaces the substitution string that has a substitution number of 2, and so on." Technically, this sentence should be without a comma, because "and so on" is a dependent clause, but if you remove the comma, you cause ambiguity... is the substitution number "2 and so on"?
• Alternatively, you could do away with both the comma and the conjunction and use a semi-colon to join two independent clauses (clauses that could stand alone as sentences). You'd typically do this if the clauses are so closely related that separate sentences might not be appropriate.
Hope this helps.
_________________ Glenn Murray
Director
Divine Write Copywriting Pty Ltd
http://www.divinewrite.com
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