“That the human mind has a certain order of possible progress, in which some things must precede others, an order which governments and public instructors can modify to some, but not to an unlimited extent: That all questions of political institutions are relative, not absolute, and that different stages of human progress not only will have, but ought to have, different institutions: That government is always either in the hands, or passing into the hands, of whatever is the strongest power in society, and that what this power is, does not depend on institutions, but institutions on it: That any general theory or philosophy of politics supposes a previous theory of human progress, and that this is the same thing with a philosophy of history.”

And this is the Origin of every Kind of Subjection; which feels itself more or less alleviated, in Proportion to the Situation of the Subjects.And, consequently, as the Law of Nature commands Us to take as much Care, as lies in Our Power, of the Prosperity of all the People; we are obliged to alleviate the Situation of the Subjects, as much as sound Reason will permit. And therefore, to shun all Occasions of reducing People to a State of Slavery, except the utmost Necessity should inevitably oblige us to do it; in that Case, it ought not to be done for our own Benefit; but for the Interest of the State: Yet even that Case is extremely uncommon. Of whatever Kind Subjection may be, the civil Laws ought to guard, on the one Hand, against the Abuse of Slavery, and, on the other, against the Dangers which may arise from it.
Proposals for a New Law Code (1768)

Speech in Vaduz (15 January 1972), quoted in The Common Market: Renegotiate or Come Out (Elliot Right Way Books, 1973), pp. 30–31
1970s

Source: http://www.friesian.com/quotes.htm Pennsylvania Gazette], Feb. 20, 1788.

https://www.newspapers.com/newspage/41022229, archived image from newspapers.com, Pennsylvania Gazette, Feb. 20, 1788 page 2 column 2

Speech to the Consultative Assembly of the Council of Europe, Strasbourg, France (23 January 1967), quoted in The New York Times (24 January 1967), p. 12.
Prime Minister

Remarks by President Obama and Prime Minister Abe of Japan at Hiroshima Peace Memorial at Hiroshima Peace Memorial in Hiroshima, Japan (May 27, 2016) https://www.whitehouse.gov/the-press-office/2016/05/27/remarks-president-obama-and-prime-minister-abe-japan-hiroshima-peace
2016
Context: There are many sites around the world that chronicle this war -- memorials that tell stories of courage and heroism; graves and empty camps that echo of unspeakable depravity. Yet in the image of a mushroom cloud that rose into these skies, we are most starkly reminded of humanity’s core contradiction; how the very spark that marks us as a species -- our thoughts, our imagination, our language, our tool-making, our ability to set ourselves apart from nature and bend it to our will -- those very things also give us the capacity for unmatched destruction. [... ] Science allows us to communicate across the seas and fly above the clouds; to cure disease and understand the cosmos. But those same discoveries can be turned into ever-more efficient killing machines. The wars of the modern age teach this truth. Hiroshima teaches this truth. Technological progress without an equivalent progress in human institutions can doom us. The scientific revolution that led to the splitting of an atom requires a moral revolution, as well.

The Rise and Fall of the Confederate Government

The Value of Science (1955)
Context: The scientist has a lot of experience with ignorance and doubt and uncertainty, and this experience is of very great importance, I think. When a scientist doesn’t know the answer to a problem, he is ignorant. When he has a hunch as to what the result is, he is uncertain. And when he is pretty darn sure of what the result is going to be, he is still in some doubt. We have found it of paramount importance that in order to progress we must recognize our ignorance and leave room for doubt. Scientific knowledge is a body of statements of varying degrees of certainty — some most unsure, some nearly sure, but none absolutely certain. Now, we scientists are used to this, and we take it for granted that it is perfectly consistent to be unsure, that it is possible to live and not know. But I don’t know whether everyone realizes this is true. Our freedom to doubt was born out of a struggle against authority in the early days of science. It was a very deep and strong struggle: permit us to question — to doubt — to not be sure. I think that it is important that we do not forget this struggle and thus perhaps lose what we have gained.

Source: Speech http://hansard.millbanksystems.com/commons/1848/feb/22/expenditure-of-the-country in the House of Commons (22 February 1848).

Source: (1776), Book V, Chapter I, Part II, 775.