A differential equation is a complicated equation which expresses certain formulas of constant relationships and in which changes in the value or magnitude assigned to certain variable factors determine the value or magnitude of the other variable factors. These equations are helpful in solving many problems of higher mathematics and the natural sciences because the knowledge of certain known factors permits one to compute the value or magnitude of the unknown variable factors. Such equations are of no help in solving problems of human action (economics) because there is no certainty of constant relationships between the values of different factors.
- Percy L. Greaves, Jr. "Mises Made Easier ", 1974. Referenced 2014-07-01.