A short and intuitive proof of Marshall's Rule

When the price of an input factor to a production process increases, then the optimal output level declines and the input is substituted by other factors. Marshall's rule is a formula that determines the own-price elasticity for one factor as a weighted sum of the elasticities of output market demand and factor substitution. This note offers a proof for Marshall's rule that is significantly shorter and somewhat more intuitive than existing derivations. Copyright Springer-Verlag Berlin Heidelberg 2003