"[E]ven in the most precise part of science, in mathematics, we cannot avoid using concepts that involve contradiction…"

"The physicist may be satisfied when he has the mathematical scheme and knows how to use for the interpretation of the…"

"The law of causality is no longer applied in quantum theory and the law of conservation of matter is no longer true f…"

"[S]ets of concepts... defined in physics. ...[F]our systems... have ...attained ...final form. The first ...Newtonian…"

"The existing scientific concepts cover always only a very limited part of reality, and the other part that has not ye…"

"Whenever we proceed from the known into the unknown we may hope to understand, but we may have to learn at the same t…"

"Modern positivism...expresses criticism against the naïve use of certain terms... by the general postulate that the q…"

"The words "position" and "velocity" of an electron... seemed perfectly well defined... and in fact they were clearly …"

"Any concepts or words which have been formed in the past through the interplay between the world and ourselves are no…"

"I remember discussions with Bohr which went through many hours till very late at night and ended almost in despair; a…"