“A difficulty in seeking Truth is the notion that certain men are ordained of heaven to seek Truth for all mankind and that we are to accept their acquisitions in the place of seeking for ourselves. We can never attain Truth by proxy. By divine ordination every man is an original investigator of Truth. He denies his own reason who hands over his religious views and opinions to any priest or religious teacher… We are to accept nothing on the opinions of others. What another man has thought and believed, what a Church Council or synod has formulated is nothing to me, only that it may be a reason for personal investigation ending in acceptance or rejection as I may find it in harmony with reason and well established truth.”

He must examine tests and explanations with the greatest precision and question them from all angles and aspects.
Ehsan Masood, Science and Islam https://www.amazon.com/Science-Islam-History-Icon/dp/1785782029/ref=sr_1_3?s=books&ie=UTF8&qid=1544708566&sr=1-3&keywords=ehsan+masood p: 169

Introduction.
Race and Democratic Society (1945)

As quoted in A Crowd of One: The Future of Individual Identity (2007) by John Clippinger, p. 130
Compare: "The distinguishing property of man is to search for and to follow after truth." – De Officiis, Book I, 13
Disputed

Source: [Jarvey, Natalie, December 4, 2017, Morgan Freeman, Kerry Washington Celebrate "Oscars of Science'" at Breakthrough Prize Ceremony, https://www.hollywoodreporter.com/news/morgan-freeman-kerry-washington-celebrate-oscars-science-at-breakthrough-prize-ceremony-1064160, The Hollywood Reporter, Los Angeles, December 4, 2017]

Life-Line (p. 16)
Short fiction, The Past Through Tomorrow (1967)

The Crystal Spirit : A Study of George Orwell (1966), Ch. I : The Man I Remembered, p. 3
Context: Orwell can only be understood as an essentially quixotic man. … He defended, passionately and as a matter of principle, unpopular causes. Often without regard to reason he would strike out against anything which offended his conceptions of right, justice and decency, yet, as many who crossed lances with him had reason to know, he could be a very chivalrous opponent, impelled by a sense of fair play that would lead to public recantation of accusations he had eventually decided were unfair. In his own way he was a man of the left, but he attacked its holy images as fervently as he did those of the right. And however much he might on occasion find himself in uneasy and temporary alliance with others, he was — in the end — as much a man in isolation as Don Quixote. His was the isolation of every man who seeks the truth diligently, no matter how unpleasant its implications may be to others or even to himself.

The Way In (2000)

1790s, First Principles of Government (1795)
Context: It is never to be expected in a revolution that every man is to change his opinion at the same moment. There never yet was any truth or any principle so irresistibly obvious that all men believed it at once. Time and reason must cooperate with each other to the final establishment of any principle; and therefore those who may happen to be first convinced have not a right to persecute others, on whom conviction operates more slowly. The moral principle of revolutions is to instruct, not to destroy.

Wir sind im Wesentlichen noch dieselben Menschen, wie die des Zeitalters der Reformation: wie sollte es auch anders sein? Aber dass wir uns einige Mittel nicht mehr erlauben, um mit ihnen unsrer Meinung zum Siege zu verhelfen, das hebt uns gegen jene Zeit ab und beweist, dass wir einer höhern Cultur angehören. Wer jetzt noch, in der Art der Reformations-Menschen, Meinungen mit Verdächtigungen, mit Wuthausbrüchen bekämpft und niederwirft, verräth deutlich, dass er seine Gegner verbrannt haben würde, falls er in anderen Zeiten gelebt hätte, und dass er zu allen Mitteln der Inquisition seine Zuflucht genommen haben würde, wenn er als Gegner der Reformation gelebt hätte. Diese Inquisition war damals vernünftig, denn sie bedeutete nichts Anderes, als den allgemeinen Belagerungszustand, welcher über den ganzen Bereich der Kirche verhängt werden musste, und der, wie jeder Belagerungszustand, zu den äussersten Mitteln berechtigte, unter der Voraussetzung nämlich (welche wir jetzt nicht mehr mit jenen Menschen theilen), dass man die Wahrheit, in der Kirche, habe, und um jeden Preis mit jedem Opfer zum Heile der Menschheit bewahren müsse. Jetzt aber giebt man Niemandem so leicht mehr zu, dass er die Wahrheit habe: die strengen Methoden der Forschung haben genug Misstrauen und Vorsicht verbreitet, so dass Jeder, welcher gewaltthätig in Wort und Werk Meinungen vertritt, als ein Feind unserer jetzigen Cultur, mindestens als ein zurückgebliebener empfunden wird. In der That: das Pathos, dass man die Wahrheit habe, gilt jetzt sehr wenig im Verhältniss zu jenem freilich milderen und klanglosen Pathos des Wahrheit-Suchens, welches nicht müde wird, umzulernen und neu zu prüfen.
Section IX, "Man Alone with Himself" / aphorism 633
Human, All Too Human (1878), Helen Zimmern translation