Sermon (1899)
“The first duty of a man is the seeking after and the investigation of truth.”
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
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Marcus Tullius Cicero 180
Roman philosopher and statesman -106–-43 BCRelated quotes
“To know the Truth, to love the Truth, and to live the Truth is the whole duty of man.”
Sermon (1899)

“The first duty of a man is to think for himself”
“The truth every man and woman seeks is in themselves.”
The Way In (2000)

Where Is Science Going? (1932)
Source: Where is Science Going?