Almost everyone plays the octaves in the last movement of the Waldstein as Glissandi. It is conventional for them to be played that way (and the AB edition actually marks them as glissando).
But Beethoven himself did not specify Glissando. In the manuscript he simply marked them to be played with thumb and little finger throughout. Andras Schiff says "so obviously they are to be played glissando". But that is not obvious at all. All that is obvious is that Beethoven wanted them played as octaves and not split between two hands (as some pianists like to do).
Neither is it an argument that you have to play glissandi because of the tempo. The music is plenty slow enough to play real octaves. And I prefer to play them that way.
Horowitz played separate octaves, and so did Cziffra - and made an even better job of it. But they were two of the finest pianists that ever lived. Everyone knows that they could have played glissandi if they had wanted.
But if this widely unknown, 5th-rate concert pianist (i.e. yours-truly) does the same then the audience will think that I either:
a. am ignorant of how it is "supposed" to be, or
b. am incapable of playing glissandi
They aren't likely to attribute it to a carefully thought through choice. Should I care? What should I do?
a. explain in the programme notes
b. explain in a spoken prologue
c. make a show of playing glissandi octaves in a warm-up
d. take Claudio Arrau's approach - just play it the way I think it should be, and be d a m n e d
