"The theory to be developed in the following pages stands directly opposed to all attempts to operate with the ideas of inductive logic. It might be described as the theory of the deductive method of testing," or as the view that a hypothesis can only be empirically tested—and only after it has been advanced," Chap. 1, A Survey of Some Fundamental Problems, pp. 6-7.

"The empirical sciences are systems of theories," Part II, Chap. 3, p. 37.

"The negation of a strictly universal statement is always equivalent to a strictly existential statement and vice versa. For examples, 'not all ravens are black' say the same thing as 'there exists a raven which is not black,' or 'there are non-black ravens,'" Part II, Chap. 3, p. 47.

"A nice adaptation of conditions will make almost any hypothesis agree with the phenomena. This will please the imagination but does not advance...