David Colander refers to how Marshall's discussion of "the art of economics--Keynes' terminology for the policy branch of economics--changes over the editions, as he gets the separate field of economics established."

Actually the term art (of economics) may be traced back to John Stuart Mill. In his "On the Definition of Political Economy...",Mill wrote:


"...the essentially distinct, though closely connected, ideas of
science and art. These two ideas differ from one another as the understanding
differs from the will, or as the indicative mood in grammar
differs from the imperative. The one deals in facts, the other in precepts.
Science is a collection of truths; art a body of rules, or directions for
conduct. The language of science is, This is, or, This is not; This does,
or does not, happen. The language of art is, Do this; Avoid that. Science
takes cognizance of a phenomenon, and endeavours to discover its law;
art proposes to itself an end, and looks out for means to effect it."


In making the distinction between positive-deductive science and normative science, Mill of course uses the term the science of political economy, which he differentiated from the "applications" of its analytical tools. This by implication would be the art of political economy, or the policy branch. With his unabiding interest in seeing the improvement in society, he continues:

"If, therefore, Political Economy be a science, it cannot be a collection
of practical rules; though, unless it be altogether a useless science,
practical rules must be capable of being founded upon it."


Sumitra Shah