I had a great admiration for Pigou. I thought that, in many ways, he was not only a faithful follower of Alfred Marshall, but he was also a more fert… - Paul Samuelson

The general method involved may be very simply stated. In cases where the equilibrium values of our variables can be regarded as the solutions of an extremum (maximum or minimum) problem, it is often possible regardless of the number of variables involved to determine unambiguously the qualitative behavior of our solution values in respect to changes of parameters.

Complete freedom is not definable once two wills exist in the same interdependent universe. We can sometimes find two situations in which Choice A is more free than Choice B in apparently every respect and at least as good as B in every other relevant sense. In such singular cases I will certainly throw in my lot with the exponents of individualism. But few situations are really of this simple type; and these few are hardly worth talking about, because they will already have been disposed of so easily. In most actual situations we come to a point at which choices between goals must be made: Do you want this kind of freedom and this kind of hunger, or that kind of freedom and that kind of hunger? I use these terms in a quasi-algebraic sense, but actually what is called "f reedom" is really a vector of almost infinite components rather than a one-dimensional thing that can be given a simple ordering.

Mathematics is the handmaiden of the sciences. But mathematics also has a life of her own, gaining as much in her own development and fulfillment from the sciences as she gives to them. To help describe how apples and planets fall, and how ropes hang, Newton and Leibniz developed the calculus. By serendipity, that mode of analysis permitted economists to perfect the theory of general equilibrium two centuries later.