When and when not to use ' and "

I noticed today when I was using mysql_fetch_array something weird happened. Database: | id | 1 Code: $colVal = "id"; $foo=mysql_fetch_array($someresult, MYSQL_ASSOC); Now all I wanted to do was get the value of 1 into the variable $bar. Please assume $someresult was the direct product of mysql_query("select * from thistable");. $bar = $foo['$colVal']; // didn't work $bar = $foo['{$colVal}']; // didn't work $bar = $foo[$colVal]; // worked $bar = $foo['id']; // obviously worked What I don't understand is why the first or second option didn't work. Can anybody shed some light on this? Brian Seymour AeroCoreProductions http://www.aerocore.net/