The observer, when he seems to himself to be observing a stone, is really, if physics is to be believed, observing the effects of the stone upon himself. Thus science seems to be at war with itself: when it most means to be objective, it finds itself plunged into subjectivity against its will. Naive realism leads to physics, and physics, if true, shows that naive realism is false. Therefore naive realism, if true, is false; therefore it is false. And therefore the behaviourist, when he thinks he is recording observations about the outer world, is really recording observations about what is happening in him.
Source: An Inquiry into Meaning and Truth, 1940,Introduction.
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