The (j) conclusion, which is derived by deduction, is combined at the stage (l) checking with (k) the data that was obtained empirically in (a). If the two agree within a degree of error allowed in the process of proceeding from (f) to (g), the assumptions will be preserved as tentatively true. If the extent of disagreement is larger than the allowed degree of error, then it becomes necessary to go to (m) modifying hypotheses by regarding some of the assumptions as wrong. In order to assign the reason for the disagreement only to a stage (f), the process from (e) to (j) must have been consistently based on deductive logic. this requirement is an important reason for using demonstration or proof in mathematics.