Young students generally think that above the bass clef comes the tenor, higher up still the alto, and above all; the treble clef, whereas all four clefs are part of the great stave.
As before stated it is usual to carry the bass clef as far up as A above three leger lines, this is really the treble A, and not an octave lower.
The following passage will show the necessity for this, and also the need of an intermediate clef, between the bass and treble.
Any pianist of ordinary ability would be able to play the above passage at sight, without the slightest difficulty, and according to theory it is correctly written. Now, if written for the violoncellist in one stave, according to the same rules, it would be extremely difficult to read at sight, the abrupt changes of clef being very confusing.
It would be possible to write this passage entirely in the tenor clef, using only three leger lines above.