In this paper I investigate Hilary Putnam’s conception of scientific realism by examining the so-called “no miracles argument.” According to a widespread reconstruction of his thought, Putnam has been moving from scientific realism, through internal realism to natural realism of common sense. Nonetheless, I show that, in fact, the American philosopher has always been a scientific realist. This notion needs however to be made clearer, because Putnam tends to move constantly on the razor’s edge between metaphysical realism and anti-realism. I argue that Putnam’s mature conception of scientific realism can be thought of as “open realism,” insofar as it is the result of the combination of the acceptable intuitions of metaphysical realism, with conceptual relativity, natural realism and pragmatism.