Sensory perceptions are signs whose meaning it is the task of our understanding to learn.

The originator of a new concept finds, as a rule, that it is much more difficult to find out why other people do not understand him than it was to discover the new truth.

Natural forces are measurable only in the form in which we know them, and the measure of their effect is energy.

Philosophy of science is philosophy enough.

-- Willard Van Orman Quine

Do not block the way of inquiry.

-- Charles Sanders Peirce

A theory which is not refutable by any conceivable event is non-scientific.

-- Karl Popper

Observation always involves theory.

-- Edwin Hubble

Mathematics is the alphabet in which God has written the universe.

-- Galileo Galilei

I have no patience with the hypothesis - often implied in tales meant to teach children to be good - that babies are born pretty much alike, and that the only agencies creating differences between boy and boy, or man and man, are steady application and moral effort.

-- Francis Galton