It is argued that Beethoven used a system of numbers to guide aspects
of many of his works, especially major ones. The numbers manifest them
selves in the number of notes in a melody and/or of bars in a work or
part of it, in groupings and numberings of works of a given kind, and
in his deliberate choice of Opus numbers. They are not only small ones
such as 3 (an important case), which of course turn up frequently any
way; larger ones are prominent, particularly 27,30,32 and 33. The inte
rpretation of the numbers was not his own innovation, but came largely
from Christian and Masonic traditions in Austria at that time; the mo
des of his adhesion to those movements is appraised. The thesis confro
nts the apparent fact that Beethoven was very bad at arithmetic; consi
deration of this matter involves the psychology of arithmetic. It also
faces a remarkable level of modern ignorance, including among musicol
ogists, of numerology and of its methods of research.