calculate with concepts and with propositions in the same 15 way as with
lines or forces or surfaces, etc. Naturally, it makes no sense to
measure propositions using numerical values. The calculation is,
therefore, not calculation with quantities and numbers. But, as we
already said, they do not belong to the essence of calculation. To
calculation only belongs being purely logically deduced.
Edmund Husserl, INTRODUCTION TO LOGIC AND THEORY OF KNOWLEDGE, 78