"All men suppose what is called Wisdom to deal with the first causes and the principles of things; so that, as has bee…"

"Practical life is not necessarily directed toward other people, as some think; and it is not the case that practical …"

"Never call yourself a philosopher, nor talk a great deal among the unlearned about theorems, but act conformably to t…"

"A light was kindled amongst the investigators of nature when Galilei let balls of a definite weight roll down the inc…"

"Theory is in itself of no use, except in so far as it makes us believe in the connection of phenomena."

"Theories usually result from the precipitate reasoning of an impatient mind which would like to be rid of phenomena a…"

"All competent thinkers agree with Bacon that there can be no real knowledge except that which rests upon observed fac…"

"It is clear that the arm of criticism cannot replace the criticism of arms. Material force can only be overthrown by …"

"If any theories or opinions of mine can be damaged by facts, so much the worse for my theories."

"[T]he studies preliminary to the construction of a great theory should be at least as deliberate and thorough as thos…"