  Much depends here on what Hacking means by “determined.” If he means entailed then one must agree with him. It is doubtful that the world, or more properly, what we can learn about it, entails a unique theory. If not, as seems more plausible, he means that the way the world is places no restrictions on that successful science, then the rationalists disagree strongly. They want to argue that the way the world is restricts the kinds of theories that will fit the phenomena, the kinds of apparatus we can build, and the results we can obtain with such apparatuses. To think otherwise seems silly. Consider a homey example.  It seems highly unlikely that someone can come up with a successful theory in which objects whose density is greater than that of air fall upwards. This is not a caricature of the view Hacking describes. Describing Pickering’s view, he states, “Physics did not need to take a route that involved Maxwell’s Equations, the Second Law of Thermodynamics, or the present values of the velocity of light (p. 70).” Although one may have some sympathy for this view as regards Maxwell’s Equations or the Second Law of Thermodynamics, one may not agree about the value of the speed of light. That is determined by the way the world is. Any successful theory of light must give that value for its speed.