Restoring Continuity in Theory Change: The Kepler-to-Newton Case

In the on-going debate between scientific realism and its various opponents, a crucial role in challenging the realist claim that success of scientific theories must be attributed to their approximate truth is played by the so-called pessimistic meta-induction: Arguing that the history of science boils down to a succession of theories which, though successful at a time, were eventually discarded only to be replaced by alternative theories which in turn met with the same fate, it purports to show that the empirical success of scientific theories cannot have any bearing on claims about their truth-likeness. Yet, the same historical record suggests a possible strategy to counter this argument. Far from being a barren wasteland, it contains cases which point to the need of adopting a selective attitude when passing judgments about truth-likeness of theories. In this vein, Psillos has proposed the so-called divide et impera move. It consists in pointing out that responsibility for the success of a theory should be attributed to an indispensable core element in it, acting in unison with other elements reflecting the concrete historical conditions under which the theory was formulated. In what follows it is argued that the discovery of Kepler’s first two laws and the transition to Newtonian mechanics provides a notable case to exhibit the divide et impera move. All the more so, since—as will be shown—Kepler himself employs a variant of this move, a fact that sheds light on the philosophical implications of his theories. As a result, it will be argued that the appropriate selective attitude towards theories becomes solidly warranted if wedded to the diachronic element in the process of a theory’s development.