Black Tie

If you are invited to a an affair that says black tie, the only proper dress for that occasion is a tuxedo.

You cannot get away with a dark suit or sport coat.

Black Tie Optional

If you are going to an event that is black tie optional, this means you either wear a tuxedo or a dark conservative suit.

A sport coat is not appropriate.

Dressy Casual

If you are attending an event that is dressy casual attire you should wear dress slacks and a dressy sport shirt like Tommy Bahama or Nat Nast, a sport coat or a dressy sweater would be optional and a nice pair of Johnson & Murphy Loafers.

Not a pair of suit pants and a dress shirt that you unbottoned the top button, and lace-up suit shoes.

Casual

If the event is casual then depending on the time of year a Tommy Bahama or Tundra sweater with Casual Bill's Kaki pants or Corduroys or for summer a nice pair of kaki or Tori Richards Tencil shorts and Tommy Bahama deck shoes.