The material which a scientist actually has at his disposal, his laws, his experimental results, his mathematical techniques, his epistemological prejudices, his attitude towards the absurd consequences of the theories which he accepts, is indeterminate in many ways, ambiguous, and never fully separated from the historical background. This material is always contaminated by principles which he does not know and which, if known, would be extremely hard to test.

Pg. 66. - Against Method (1975)