Precedence question- cookie value over form value?

Hi PHPers, If I have a script that checks to see if a variaable is defined. The variaable is from a form and is sent to the script. There is also a cookie that may be set with a name as the same name as from the form. When the script checks and assuming the cookie is set and a value sent from the form , which value does the variable take on? Thanks Dexter