• Whenever a theory appears to you as the only possible one, take this as a sign that you have neither understood the theory nor the problem which it was intended to solve

    (K.R. Popper, Objective Knowledge: An Evolutionary Approach, 1972)
  • No matter how many instances of white swans we may have observed, this does not justify the conclusion that all swans are white

    (K.R. Popper, The Logic of Scientific Discovery, 1934)
  • Our knowledge can only be finite, while our ignorance must necessarily be infinite

    (K.R. Popper, Conjectures and Refutations: The Growth of Scientific Knowledge, 1963)