Listen to these two gentlemen- they know what they're talking about! The only thing I would add is that the dirk is worn on the right hand side and the sword on the left because the vast majority of people are right handed. The sword is meant to be used in the dominant hand and the dirk in the submissive- meaning that if you're right handed, the sword be a right-hand draw (therefore on the left side of the body) and the dirk a left handed draw (therefore on the right side of the body.) If you're left handed, they would be reversed, meaning the dirk would be a right handed draw and the sword, a left. (This is a general rule for all Western martial arts, which is different from Eastern martial arts, where all techniques are taught ambidextrous. Read the Book Of Five Rings by Miyamoto Musashi.) Now weather this has made it's way into modern formal wear or not, I can't say. But I do know that it was done that way when the weapons were used, as a matter of practicality.