gregory, My understanding of levels of formality is as follows, from least formal to most formal: 1) Dress shirt and trousers. 2) Dress shirt, odd trousers and jacket. 3) Dress shirt, jacket and tie, odd trousers. 4) Single Breasted Suit and tie (We'll assume you are wearing a shirt at this point). 5) Double Breasted Suit and Tie 6) Black Tie 7) White Tie There is certainly freedom within those levels, however, as a more conservative dresser, I would not recommend taking too many liberties. Sweaters may typically be substituted for odd jackets, with or without ties. I would not recommend wearing a tie without a jacket, as the look is one that is somewhat disheveled, in my opinion. A jacket or sweater "frames" the tie rather well, where, without a jacket or sweater, the tie seems out of place and the look is an incomplete one. Also, while I support wearing odd jackets and trousers without ties, I can't say I'm very fond of wearing a suit without a tie. I find this look overly reminiscent of a leisure suit, a fashion which I'm not fond of.