 Philosophically influential early work in this direction was done by Jeffreys and by Popper, both of whom tried to analyze simplicity in probabilistic terms. Jeffreys argued that “the simpler laws have the greater prior probability,” and went on to provide an operational measure of simplicity, according to which the prior probability of a law is \(2^{-k}\), where \(k =\) order + degree + absolute values of the coefficients, when the law is expressed as a differential equation (Jeffreys 1961, p. 47). A generalization of Jeffreys’ approach is to look not at specific equations, but at families of equations. For example, one might compare the family, LIN, of linear equations (of the form \(y = a + bx)\) with the family, PAR, of parabolic equations (of the form \(y = a + bx + cx^2)\). Since PAR is of higher degree than LIN, Jeffreys’ proposal assigns higher probability to LIN. Laws of this form are intuitively simpler (in the sense of being more elegant).