Can a wizard cast without benefit of his hands or gestures?

Can a wizard cast without speaking?

If you're going by the most recent books it seems that much if what a wizard does for a spell (props, sigils and such) are not necessary in the literal sense. Wizards need to be able to concentrate and have access to some sort of power source.  The words and the gestures serve more to get them in the right frame of mind.  So I would say a pair handcuffs and a gag wouldn't stop a wizard outright but it would most certainly add another degree of difficulty to what ever task they were trying to accomplish