This discussion paper critically reviews a new book by Aoki and Yokishawa and presents some
of the techniques adopted by the authors as a new approach to the foundations of macroeconomics.
The paper discusses some of the main techniques of statistical mechanics relevant in this context,
namely the Master Equation and the Polya Urn. The former is a key instrument for deriving some
Keynesian results throughout the book, in particular the role of effective demand in stimulating the
economy; additionally, it is used to assess the role and significance of uncertainty and to re-examine
so-called «policy ineffectiveness», showing instead the positive contribution of an active economic
policy. The Polya Urn is used to show demand saturation as a growth limiting factor and demand
for new products as a growth-enhancing one, with the clear objective of linking the Keynesian principle
of effective demand (short term) with a long-term growth theory.