“We both call in experience to the support of our opinions; but, in your case, the experience is based on vague uncertainties, whilst I, more circumspect, strive never to lose sight of those scientific principles which ought to guide the observer in all his investigations. My aim is not to defend systems, or bolster up theories; I confine myself to the citation of facts, such as society presents to our view. If these facts be legitimately established, it follows that we must accept of and accommodate our reason to them.”

Introduction à l'Étude de la Médecine Expérimentale (1865)

Cosmos: A Spacetime Odyssey (2014)

To question genetic intelligence is not racism (2007)
Context: Science is no stranger to controversy. The pursuit of discovery, of knowledge, is often uncomfortable and disconcerting. I have never been one to shy away from stating what I believe to be the truth, however difficult it might prove to be. This has, at times, got me in hot water.
Rarely more so than right now, where I find myself at the centre of a storm of criticism. I can understand much of this reaction. For if I said what I was quoted as saying, then I can only admit that I am bewildered by it. To those who have drawn the inference from my words that Africa, as a continent, is somehow genetically inferior, I can only apologise unreservedly. That is not what I meant. More importantly from my point of view, there is no scientific basis for such a belief.
I have always fiercely defended the position that we should base our view of the world on the state of our knowledge, on fact, and not on what we would like it to be. This is why genetics is so important. For it will lead us to answers to many of the big and difficult questions that have troubled people for hundreds, if not thousands, of years.
But those answers may not be easy, for, as I know all too well, genetics can be cruel. My own son may be one of its victims. Warm and perceptive at the age of 37, Rufus cannot lead an independent life because of schizophrenia, lacking the ability to engage in day-to-day activities.

Section 10 : Of Miracles Pt. 1
An Enquiry Concerning Human Understanding (1748)

Nicomachean Ethics
Source: Book I, 1098a-b; §7 as translated by W. D. Ross
Context: Let this serve as an outline of the good; for we must presumably first sketch it roughly, and then later fill in the details. But it would seem that any one is capable of carrying on and articulating what has once been well outlined, and that time is a good discoverer or partner in such a work; to which facts the advances of the arts are due; for any one can add what is lacking. And we must also remember what has been said before, and not look for precision in all things alike, but in each class of things such precision as accords with the subject-matter, and so much as is appropriate to the inquiry. For a carpenter and a geometer investigate the right angle in different ways; the former does so in so far as the right angle is useful for his work, while the latter inquires what it is or what sort of thing it is; for he is a spectator of the truth. We must act in the same way, then, in all other matters as well, that our main task may not be subordinated to minor questions. Nor must we demand the cause in all matters alike; it is enough in some cases that the fact be well established, as in the case of the first principles; the fact is the primary thing or first principle. Now of first principles we see some by induction, some by perception, some by a certain habituation, and others too in other ways. But each set of principles we must try to investigate in the natural way, and we must take pains to state them definitely, since they have a great influence on what follows. For the beginning is thought to be more than half of the whole, and many of the questions we ask are cleared up by it.

Letter to Judge John Tyler http://www.constitution.org/tj/jeff11.txt (June 28, 1804); in: The Writings of Thomas Jefferson, Memorial Edition (ME) (Lipscomb and Bergh, editors), 20 Vols., Washington, D.C., 1903-04, Volume 11, page 33
1800s, First Presidential Administration (1801–1805)

Pt. II, ch. 10, sec. 1.
1920s, Process and Reality: An Essay in Cosmology (1929)

Theories should be accredited, Aristotle insists, "only if what they affirm agrees with the facts."
Great Books: The Foundation of a Liberal Education (1954)

Letter to John Bright (14 September 1854), quoted in John Morley, The Life of Richard Cobden (London: T. Fisher Unwin, 1905), p. 626.
1850s