Scientists must use the simplest means of arriving at their results and exclude everything not perceived by the senses.

A colour is a physical object as soon as we consider its dependence, for instance, upon its luminous source, upon other colours, upon temperatures, upon spaces, and so forth.

Science always has its origin in the adaptation of thought to some definite field of experience.

I can accept the theory of relativity as little as I can accept the existence of atoms and other such dogmas.

To us investigators, the concept 'soul' is irrelevant and a matter for laughter. But matter is an abstraction of exactly the same kind, just as good and just as bad as it is. We know as much about the soul as we do of matter.

Everyone is free to set up an opinion and to adduce proofs in support of it. Whether, though, a scientist shall find it worth his while to enter into serious investigations of opinions so advanced is a question which his reason and instinct alone can decide. If these things, in the end, should turn out to be true, I shall not be ashamed of being the last to believe them.

Bodies do not produce sensations, but complexes of elements (complexes of sensations) make up bodies.