V. I. Lenin



  Materialism and Empirio-Criticism (Moscow: Foreign Language Publishing
  House, no year given)



  "The fundamental premise of materialism is the recognition of the
  external world, of the existence of things outside and independent of
  our mind." (p. 78)



  "Did Nature Exist Prior to Man? We have already seen that this
  question is particularly repugnant to the philosophy of Mach and
  Avenarius. Natural science positively asserts that the earth once
  existed in such a state that no man or any other creature existed or
  could have existed on it. Organic matter is a later phenomenon, the
  fruit of a long evolution. It follows that there was no sentient
  matter, no 'complexes of sensations,' no self that was supposedly
  'indissolubly' connected with the environment in accordance with
  Avenarius' doctrine.. Matter is primary, and thought, consciousness,
  sensation are products of a very high development. Such is the
  materialist theory of knowledge, to which natural science
  instinctively subscribes." (p. 69)



  "We have seen that the starting point and the fundamental premise of
  the philosophy of empirio-criticism is subjective idealism. The world
  is our sensation--this is the fundamental premise. . . .The absurdity
  of this philosophy lies in the fact that it leads to solipsism, to the
  recognition of the existence of the philosophising individual only."
  (p. 89)



  "Yesterday we did not know that coal tar contained alizarin. Today we
  learned that it does. The question is, did coal tar contain alizarin
  yesterday?

  "Of course it did. To doubt it would be to make a mockery of modern
  science.

  "And if that is so, three important epistemological conclusions
  follow:

  "1)Things exist independently of our consciousness, independently of
  our perceptions, outside of us, for it is beyond doubt that alizarin
  existed in coal tar yesterday and it is equally beyond doubt that
  yesterday we knew nothing of the existence of this alizarin and
  received no sensations from it.

  "2) There is definitely no difference in principle between the
  phenomenon and the thing-in-itself, and there can be no such
  difference. The only difference is between what is known and what is
  not yet known. And philosophical inventions of specific boundaries
  between the one and the other, inventions to the effect that the
  thing-in-itself is "beyond" phenomena (Kant), or that we can or must
  fence ourselves off by some philosophical partition from the problem
  of a world which in one part or another is still unknown but which
  exists outside us (hume)--all this is the sheerest nonsense, Schrulle,
  crotchet, invention.

  "3)In the theory of knowledge, as in every other branch of science, we
  must think dialectically, that is, we must not regard our knowledge as
  ready-made and unalterable, but must determine how knowledge emerges
  from ignorance, how incomplete, inexact knowledge becomes more
  complete and more exact."

  (p. 98)