"Ptolemy... against the champions of this or that cosmology of the heavens... had dared to claim that it is legitimate to interpret the facts of astronomy by the simplest geometrical scheme which will 'save the phenomena,' no matter whose metaphysics might be upset. His conception of the physical structure of the earth, however, prevented him from carrying through in earnest this principle of relativity, as his objections to the hypothesis that the earth moves amply show."

“The only way to avoid becoming a metaphysician is to say nothing.”

“With what philosophical point of view did I begin my career as teacher? Looking back to that period, I see that it was a rather inchoate form of idealism, reflecting the liberal Protestant orientation I had then adopted. This idealism was gradually revised to make room for major aspects of Deweyan instrumentalism. In my years at Columbia, Dewey had impressed me as a person, and during my decade in Chicago, in close contact with colleagues whom he had deeply influenced, I came to accept what appeared to be the core of his contribution to philosophy. But continued sensitivity to insights from various quarters prevented me from becoming a disciple of any one philosopher or philosophical school.”

“A student of the history of physical science will assign to Newton a further importance which the average man can hardly appreciate. ...the separation … of positive scientific inquiries from questions of ultimate causation.”

“The central place of epistemology in modern philosophy is no accident... Knowledge was not a problem for the ruling philosophy of the Middle Ages; that the whole world which man's mind seeks to understand is intelligible to it was explicitly taken for granted. That people subsequently came to consider knowledge a problem implies that they had been led to accept certain different beliefs about the nature of man and about the things which he tries to understand.”