when to use commas before the conjunction ‘and’

Reading the transcript of President Bush’s national address on the economy, which is posted as a news release on the official White House website, it becomes painfully clear that the presidents’ editors and aides have no clue how to use commas.

Consider the commas in these statements.

“…home loans are often packaged together, and converted into financial products called mortgage-backed securities.”

“Many investors assumed these securities were trustworthy, and asked few questions about their actual value.”

“So I’ve proposed that the federal government reduce the risk posed by these troubled assets, and supply urgently-needed money so banks and other financial institutions can avoid collapse and resume lending.”

None of these commas is needed. If no subject follows the conjunction and, then no comma should precede it. In the first example, the same subject, home loans, applies to the verbs packaged and converted. Investors assumed and asked. Lastly, the government will reduce risk and supply money.

Many people get confused about whether or not to use a comma before the conjunction and. There are four scenarios to consider, and then you’ll have it down pat.

1. If no subject follows AND, then no comma precedes it.
   EX: I finished reading the transcript and then critiqued its punctuation.
2. If the clauses joined by AND have the same subject, and they are closely related in meaning (the second being a logical result of the first), then don’t use a comma before AND.
   EX: I finished reading the transcript and then I called my friend to vent about the willy-nilly commas.
3. If the clauses joined by AND have the same subject, but they are not closely related, then use a comma before AND.
   EX: I finished reading the transcript, and then I called my friend to discuss Dancing With The Stars.
4. If the clauses joined by AND have different subjects - whether or not they are closely related - use a comma.
   EX: I critiqued the speech, and then President Bush fired his editor.