WHY IS THE ALTO CLEF USED FOR THE VIOLA?

I have no idea. I guess thats just like asking, "Why is the treble clef used for the violin?"

The purpose of the alto clef, as well as the tenor clef, is to notate a piece of music in a way so that most of the notes will be placed on the staff. In an alto clef, the center line is middle C, which is around the median of the range of a viola. If it were notated in treble clef, most of the notes would be below the staff on ledger lines, which can get rather annoying. So, the C clef in general is used in order to make the music more pleasing to the eye.

Just like the person above me said, if you werent reading the alto clef you would have a whole lotta ledger lines. Ledger lines can get very confusing, especially if you have a lot of them on one note.

I'm months, maybe even years late, but for the person above who says ledger lines aren't a big deal. I play quite a bit of instruments including Tuba and it is difficult to go from reading on the staff then playing a pedal Bb. Within a second you have to see if the ledger line goes through the note or is it on top then play that note.

It's probably too late to change now (and I'm not advocating change here), but neither the alto nor the tenor clef is really necessary. Our use of clefs is equivocal.

Consider: The bass avoids leger lines by transposing the bass clef down an octave. The piccolo avoids leger lines by transposing the treble clef up an octave.

It isn't true that octave transposition is confined to instruments with extreme ranges, however: The guitar and the tenor voice avoid leger lines by transposing the treble clef down an octave.

Consider further: The viola is tuned precisely like a cello only an octave higher. The cello uses the bass clef. Why couldn't the viola avoid leger lines by transposing the bass clef up an octave? In fact, it could--very easily.