[quote name='Joebass' post='1159231' date='Mar 12 2011, 12:56 PM']Sorry, but you're wrong there. It's exactly the same principle as woodwind instruments, i.e. so that the player doesn't have to sight transpose or learn new fingerings/positions.
Logically, if you describe a bass in standard tuning as being at concert pitch, then a bass tuned down a half step would be in Db and the necessary transposition would need to be made to the score.[/quote]
I see what you're saying and obviously when I write trumpet or sax parts etc the keys are transposed, but if, say, you drop the E string to a D, why does that change the key for the bass? All the other strings are in concert pitch and you may only visit the (lower) D string twice in the whole piece.
Changing the key for the piece would mean you're fine on one string but then have to learn new fingerings for the other 3 (or 4 or 5).