“In truth, I swore to support the Constitution because I believe in it. I do not believe in their construction of it. It is as well known as any historical fact can be known, that the framers of the Constitution so worded it as that it never should recognize the idea of slave property. From the beginning to the ending of it.”

As quoted in His Brother's Blood: Speeches and Writings, 1838–64 https://books.google.com/books?id=qMEv8DNXVbIC&pg=PA193&lpg=PA199 (2004), edited by William Frederick Moore and Jane Ann Moore, p. 199
1860s, Speech to the U.S. House of Representatives (April 1860)

2000s, The Real Abraham Lincoln: A Debate (2002), Q&A

ThurgoodMarshall.com, Speeches. Constitutional Speech http://www.thurgoodmarshall.com/speeches/constitutional_speech.htm (May 6, 1987)

Address to the British Association for the Advancement of Science (1898)
Context: No incident in my scientific career is more widely known than the part I took many years ago in certain psychic researches. Thirty years have passed since I published an account of experiments tending to show that outside our scientific knowledge there exists a Force exercised by intelligence differing from the ordinary intelligence common to mortals. This fact in my life is, of course, well understood by those who honored me with the invitation to become your president. Perhaps among my audience some may feel curious as to whether I shall speak out or be silent. I elect to speak, although briefly. … To ignore the subject would be an act of cowardice — an act of cowardice I feel no temptation to commit.
To stop short in any research that bids fair to widen the gates of knowledge, to recoil from fear of difficulty or adverse criticism, is to bring reproach on science. There is nothing for the investigator to do but to go straight on; "to explore up and down, inch by inch, with the taper his reason; "to follow the light wherever it may lead, even should it at times resemble a will-o'-the-wisp. I have nothing to retract. I adhere to my already published statements. Indeed, I might add much thereto. I regret only a certain crudity in those early expositions which, no doubt justly, militated against their acceptance by the scientific world. My own knowledge at that time scarcely extended beyond the fact that certain phenomena new to science had assuredly occurred, and were attested by my own sober senses and, better still, by automatic record. I was like some two-dimensional being who might stand at the singular point of a Riemann's surface, and thus find himself in infinitesimal and inexplicable contact with a plane of existence not his own.
I think I see a little farther now. I have glimpses of something like coherence among the strange elusive phenomena; of something like continuity between those unexplained forces and laws already known. This advance is largely due to the labors of another association, of which I have also this year the honor to be president — the Society for Psychical Research. And were I now introducing for the first time these inquiries to the world of science I should choose a starting point different from that of old. It would be well to begin with telepathy; with the fundamental law, as I believe it to be, that thoughts and images may be transferred from one mind to another without the agency of the recognized organs of sense — that knowledge may enter the human mind without being communicated in any hitherto known or recognized ways.

1997 Senate confirmation hearing, reported in Deborah Tedford, " "Senate Will Have To Confirm Court Choice http://www.npr.org/templates/story/story.php?storyId=104532843&ft=1&f=3", NPR (26 May 2009).

Galaxies, Nuclei, and Quasars, Harper and Row, New York, 1965

Source: Children of the Mind

14 January letter to John Martin: 14, Correspondence between John Martin and William Smith O'Brien relative to a French invasion, 1861 https://books.google.com/books?id=uioenbWx30MC&pg=PA14,

1850s, The Present Aspect of the Slavery Question (1859)
Context: Our fathers, therefore, were fully alive to the scope of their words and their work; and thus, as I believe, the Constitution of the United States, in its essential spirit and intention, recognizes the essential manhood of Dred Scott as absolutely as it does that of the President, of the Chief Justice, or of any Senator of the United States. I think I have not unfairly stated the spirit of the age, the sentiments of the fathers, and the original doctrine of this government upon the question of slavery. The system was recognized by law, but it was considered an evil which Time was surely removing. And, as if to put this question at rest forever, to show that the framers of this government did not look forward to a continuance of slavery, Mr. Stephens of Georgia, the most sagacious of the living slavery leaders, says, in June of this year, 'The leading public men of the South, in our early history, were almost all against it. Jefferson was against it. This I freely admit, when the authority of their names is cited. It was a question which they did not, and perhaps could not, thoroughly understand at that time'.