Bill Phillips made a fundamental contribution to dynamic stabilisation policy and to the application of control methods to this issue. His contribution is contained in chapters 16 and 17, a pair of essays originally published in the Economic Journal. These essays draw upon his background as an engineer and are the first papers to apply feedback control methods to the stabilisation of a macroeconomy. Today that is a burgeoning field, and despite certain challenges stemming from the subsequent development of rational expectations, the application of control methods is now an integral part of the analysis of dynamic economic systems. In fact the Society of Economic Dynamics and Control (now the Society of Economic Dynamics) and the Journal of Economic Dynamics and Control, originally developed in 1979 to foster the application of control methods to economics, are both now firmly established within the profession.

Phillips' contribution, like many fundamental contributions, was a simple one. Previously, Samuelson (1939) and Hicks (1950) had shown how if one combines the multiplier in consumption with the accelerator in investment, one can derive a dynamic equation determining the evolution of national income (output). The precise nature of this dynamic relationship depends upon the types of lags one considered and many variants of such relationships are possible. The dynamics can be expressed in discrete time, as by Samuelson and Hicks, or in continuous time, as for example illustrated by R.G.D. Allen (1956) and used by Phillips himself.