Why did Putnam think the success of science would be hard to explain without realism?

Hilary Putnam argued that the success of science would be impossible to explain without scientific realism. This position, often referred to as the "no-miracle" argument, was directed against the logical positivists, who viewed scientific theories merely as predictive instruments rather than descriptions of an independently existing reality.1

Putnam contended that if successful scientific theories were not understood as describing an independently existing reality, their systematic success—such as the ability to compute reaction energies with extraordinary accuracy—would be a "coincidence of cosmic proportions," or a "sheer miracle". By maintaining that theories are at least approximately true, realists can account for the effectiveness of scientific practice in a way that antirealist or instrumentalist views cannot. This argument highlights the realist conviction that the predictive power and practical applications of science are best explained by the fact that our theories successfully track features of the objective world.213