Rule of Three

Abstract

Next is (dealt with) the ‘rule of three’. Suppose a composite thing has two parts. Suppose also that there is a relationship between the parts to the effect that if one part is of a certain measure, the other would be of a fixed corresponding measure. Suppose also that this relationship is known. In such a situation the method of inferring, in another composite elsewhere, the measure of one part (when the other is known), is termed as the ‘rule of three’. (To cite) an example: When it is known that 5 measures of paddy will yield 2 measures of rice, it can be presumed that this relationship in measures between paddy and rice persists everywhere. Hence, if it is desired to know how many measures of rice would be got from 12 measures of paddy, this ‘rule of three’ procedure is made use of. Here, in the calculation of rice for 12 measures of paddy, the known measure, 5, is termed pramāṇa (antecedent or argument). The corresponding rice, 2 measures, is termed pramāṇa-phala (consequent or fruit). 12 measures of paddy is termed icchā, and the corresponding measure of rice, which is to be found out, is termed icchā-phala (resultant or required fruit).