Why did Hilary Putnam first propose that logic could be empirical?

Hilary Putnam first proposed that logic could be empirical as part of an effort to provide a realist interpretation of quantum mechanics.1

Many physicists view quantum mechanics not as a representation of the actual physical state of a system, but merely as an algorithm for calculating measurement probabilities. To counter this, Putnam argued that quantum mechanics does represent real physical states; however, he posited that the logical rules required for quantum calculations diverge from those used in classical physics. By suggesting that logic is empirical, he sought to reconcile the theory with a realist perspective.1

Putnam eventually renounced this radical approach, later adopting a version of quantum mechanics developed by David Bohm and others.1