 The logical positivists faced a hard dilemma when trying to make sense of science. On the one hand, they thought that all meaningful talk was ultimately talk about observables. On the other hand, they respected science enough to deny that talk of unobservables was meaningless. The solution was to ‘locate’ the unobservables in the observation language; in other words, to find a way to reduce talk of unobservables to talk about observables.