ABSTRACT
The operations considered so far in relation to areas or plane measurement, and likewise those relating to volume or three-dimensional space, were of two kinds only. Either they were reducible to logical addition and subtraction or else they were logical but not numerical multiplications. Frequently, the elements and relations involved were such as could be expressed in quantitative terms, but the problem of calculating an area in such terms is one which we have not yet considered. This question involves mathematical multiplication, which goes beyond logical multiplication: a rectangle measuring 2 × 3 linear units gives six square units.
