In this recent London Lounge thread, Nicholas Antongiovanni, author of The Suit, has ably furnished what might be the single best all-in-one guide to wedding attire from the bridegroom's prospective. It's also an excellent, well-illustrated primer on the essential distinctions between day and evening semi-formal and formal wear. Didactic interventions like these may help thwart further erosion in observing the old rule of "dressing for the occasion."