It has become of great interest to inquire into the history of what Whitehead called « bifurcation of nature ». This history is possible provided we connect art history with science history to dig into the reasons why the distinction between primary and secondary qualities has been thought so central since the time of Locke all the way to the present debates around « naturalism ». Those lectures try to sketch this history, thus defining a second empiricism in the line of the one proposed by William James, one that is defined more by « matters of concern » than by « matters of fact », whose very peculiar aesthetics is being explored.