Quotes about possibility
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Fothergill v. Rowland (1873), L. R. 17 Eq. Ca. 139.

Writing as his character, "th' Hon. Ex.-Editur Cale Fluhart." as quoted in The American Humorist : Conscience of the Twentieth Century (1964) by Norris W. Yeats, p. 107.

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At That Point in Time, Loyalty to Baker

1970's, Every Man an Artist: Talks at Documenta 5', 1972
Source: How to Stop Worrying and Start Living (1948), p. 14

Letter to Thomas Jefferson, 6 October 1800 http://founders.archives.gov/documents/Jefferson/01-32-02-0120,” Founders Online, National Archives. Source: The Papers of Thomas Jefferson, vol. 32, ed. Barbara B. Oberg. Princeton: Princeton University Press, 2005, pp. 204–207

The Austrians Were Right, November 20, 2008 http://www.house.gov/apps/list/speech/tx14_paul/statement_11_20_08.shtml http://www.youtube.com/watch?v=8PIEGK0IbA4
2000s, 2006-2009
Source: Being Vegan (2000), p. 43
Source: The Romantic Generation (1995), Ch. 3 : Mountains and Song Cycles

“I'm a pessimist about probabilities, I'm an optimist about possibilities.”
As quoted in "Lewis Mumford Remembers" by Carey Winfrey in The New York Times (6 July 1977)
Source: 1960s - 1970s, The Design of Inquiring Systems (1971), p. 13; cited in Jong S. Jun, Frank P. Sherwood (2007) The Social Construction of Public Administration. p. 76

Page 13
Conversation: Elon Musk on Wired Science (2007), Foreword to Marc Kaufman's Mars Up Close: Inside the Curiosity Mission https://books.google.com/books/about/Mars_Up_Close.html?ido6XaCwAAQBAJ&hlen. National Geographic. ISBN 978-1-4262-1278-9.

Interview https://www.newstatesman.com/politics/2015/01/winston-churchill-new-statesman-archive with Kingsley Martin for the New Statesman (7 January 1939)
The 1930s

" " (nothing) published in the Personal Journal of Shalosh B. Ekhad and Doron Zeilberger

“The fact that you are not sure means that it is possible that there is another way someday.”
lecture II: "The Uncertainty of Values"
The Meaning of It All (1999)

Quote from John Constable's letter to C.R. Leslie (March 1833), from The Letters of John Constable, R.A. to C. R. Leslie, R.A. 1826-1837 (Constable & Co., 1931), p. 104
1830s

"Quotes", Anatomy of Criticism: Four Essays (1957), Anagogic Phase: Symbol as Monad
“Domination” (1908), in On Individuality and Social Forms (1971), pp. 113-114

Letter to the “Mayor, Aldermen, and Commons of the city of York” again as Lord Protector, June 1483, reprinted in Richard the Third (1956) http://books.google.com/books?id=dNm0JgAACAAJ&dq=Paul+Murray+Kendall+Richard+the+Third&ei=TZHDR8zXKZKIiQHf2NCpCA

Babbage in November 1839, recalling events in 1821; quoted in Harry Wilmot Buxton and Anthony Hyman (1988), Memoir of the Life and Labours of the Late Charles Babbage. "Computers" here refers to people calculating by hand.
Brahman and the Universe (1978), in Minor Works II (2001), p. 62
Listening to the Land
Grassé, Pierre Paul (1977); Evolution of living organisms: evidence for a new theory of transformation. Academic Press, p. 2-3
Evolution of living organisms: evidence for a new theory of transformation (1977)
Source: From the Notebooks of Dr. Brain (2007), Chapter 2 “Facing the Ultimate Archenemy” (p. 58)

“Ambassador Zhou Wenzhong, welcome! Your great country [of China] makes our Happy Meals possible!”
White House Correspondents' Association Dinner (2006)

Thesis and Antithesis http://whitewolf.newcastle.edu.au/words/authors/C/CloughArthurHugh/verse/poemsproseremains/antithesis.html, st. 4.

1920s, The Genius of America (1924)
The Origins of Modern Science (1957) Introduction

In Encyclical Letter Spe Salvi http://www.vatican.va/holy_father/benedict_xvi/encyclicals/documents/hf_ben-xvi_enc_20071130_spe-salvi_en.html (30 November 2007)
2007

The Renaissance in India (1918)
Source: A social information processing approach to job attitudes and task design. 1978, p. 231
Source: The psychology of interpersonal relations, 1958, p. 81

As quoted in The Journal of NIH Research (1990), 2, 30
General sources

The Girl Nobody Knows; New Movie Magazine, Reginald Taviner (October 1932) http://www.irenedunnesite.com/press/new-movie-magazine-october-1932/.
Source: 1960s, Economics As A Moral Science, 1969, p. 12

but that piece of received wisdom is presupposed in every act of slander as well.
E. Lamotte: History of Indian Buddhism, Institut Orientaliste, Louvain-la-Neuve 1988 (1958), quoted in Elst, K. (2002). Who is a Hindu?: Hindu revivalist views of Animism, Buddhism, Sikhism, and other offshoots of Hinduism.

Elliot's Debates, volume 2, p. 364. (28 July 1788)

Progress, Coexistence and Intellectual Freedom (1968), Dangers, Police Dictatorships

Quote from his letter to the Dutch modern architect Oud, 24 June 1919; as quoted in Mondrian, -The Art of Destruction, Carel Blotkamp, Reaktion Books LTD. London 2001, p. 126
1912 – 1919

Aliens Cause Global Warming (2003)

1946 - 1963, interview with John Richardson' (1957)
Quoted on his facebook profile (3 April 2015)

Source: "Microeconomic systems as an experimental science," 1982, p. 923.
Gerald Bullett, "Walt Whitman" in", in Alfred Barratt Brown, Great Democrats, 1934 (reprinted by Spokesman Books, 2013).

Forward, 3 October, 1936, quoted in Talus, Your Alternative Government (London: Eyre & Spottiswoode, 1945), p. 36.

“Different types of love
are possible”
Desert Island Disk
Lyrics, A Moon Shaped Pool (2016)

Browne v. Cross (1852), 14 Beav. 113.

[Heisler, Mark, Larger Than Life, The Los Angeles Times, 1999-10-13]
Post-NBA life

Source: Fullyramblomatic Novels, Fog Juice, Chapter Two
The Pageant of Life (1964), On Promiscuity & Continence
The survival instinct tends to prolong life. The fundamental drive tends to inform itself about the universe.
Advice to Clever Children (1981)

Source: Persons and Places (1944), p. 159

Source: History of Mathematics (1923) Vol.1, p. 90

criticizing the Cambridge School of criticism, e.g. John Middleton Murry and Herbert Read, “Fine Writing,” pp. 306-307
Reperusals and Recollections (1936)

(version in original Dutch / origineel citaat van Suze Robertson:) Al is dat klassikale lesgeven ook zóó vermoeiend.. ..ik zette mijn werk plichtmatig voort, zodat wel niemand 't aan mij kon merken. Want ik leefde op het vaste voornemen: over eenige jaren ga ik schilderen. En daar spaarde ik voor, door in alles zoo sober mogelijk te wezen.
Source: 1900 - 1922, Onder de Menschen: Suze Robertson' (1912), p. 31

"Get Ready for the Battle of the Baywatch Babes", interview with TV Guide (25 March 2000) http://www.tvguide.com/news/ready-battle-baywatch-38819/.

Interview with Liz Jones http://www.dailymail.co.uk/pages/you/article.html?in_article_id=517492&in_page_id=1908, Daily Mail, March 2008

Out of Control: The New Biology of Machines, Social Systems and the Economic World (1995)

“Needs must it be hard, since it is so seldom found. How would it be possible, if salvation were ready to our hand, and could without great labour be found, that it should be by almost all men neglected? But all things excellent are as difficult as they are rare.”
Et sane arduum debet esse, quod adeo raro reperitur. Qui enim posset fieri, si salus in promptu esset et sine magno labore reperiri posset, ut ab omnibus fere negligeretur? Sed omnia praeclara tam difficilia, quam rara sunt.
Part V, Prop. XLII, Scholium
Ethics (1677)

Sun Star Manila http://www.sunstar.com.ph/manila/local-news/2015/08/18/escudero-asks-govt-stop-buying-dilapidated-military-hardware-425294
2015

Quote in Mondrian's letter to Israel Querido, Summer of 1909; published in the weekly magazine 'De Controleur' 23 Oct, 1909; as cited in English translation, in Two Mondrian sketchbooks 1912 - 1914, ed. Robert P. Welsh & J. M. Joosten, Amsterdam 1969 p. 10
1900's

Gottfried Leibniz (May, 1686) as quoted in George R. Montgomery, Tr., "Correspondence between Leibniz and Arnauld," Leibniz: Discourse on metaphysics; correspondence with Arnauld, and Monadology https://books.google.com/books?id=5-IeAQAAMAAJ (1916) VIII, p. 108

1950s, Conquering Self-centeredness (1957)
p. 27.

D. Appleton., (1887). The Popular Science Monthly, Volume 30.
Pope Francis has utterly failed to tackle the church’s abuse scandal https://www.theguardian.com/commentisfree/2018/jul/26/pope-francis-catholic-church-abuse-scandal-failed (26 July 2018), The Guardian.

Regarding the connection between his fighting of his illness (skin cancer and lymphoma) and the brothers Gärdestad's music as quoted on Kenneth Gärdestad: "Blir sista stora hurraropet", Selåker, Johannes, Expressen.SE, published on 8 February 2018 (web) https://www.expressen.se/noje/kenneth-gardestad-jag-mar-samst/

Source: Increasing Returns and Path Dependence in the Economy, (1994), p. 1: Chapter 1. Positive feedback in economics
Pierre Curie's Principle of One Way-Process (1970)

Interview on LBC TV, May 23, 2006 http://www.memritv.org/Transcript.asp?P1=1152
Quotes 2000s, 2006
"Anatomy of the Absurd" (1962), p. 104
Tynan Right and Left (1967)