Those who take this route ask what meaningful relationships between
the aggregate variables of the economy can be established starting from
a set of independent utility maximizing individuals. But, they make the
further and crucial assumption that the aggregates in question can be
considered as resulting from one aggregate, or average, rational individual’s
choices. This has not always been the case. Many earlier macroeconomists
were content to specify the relations between aggregate variables
and to test them without having recourse to models of individual behaviour.
It was nevertheless common practice to invoke individual decisions
as a way of justifying the assumptions made about the macroeconomic
relations. This explains the famous remark that ‘70% of Keynes’ General
Theory is microeconomics’. Indeed, in the most sophisticated modern
macroeconomic model, the DSGE synthesis, to which I have already
referred, the aggregation problem is not solved, just treated as if it were
solved.