Thomas Hobbes on Knowing ThyselfLeviathan, or the Matter, Forme, and Power of a Commonwealth, Ecclesiasticall and Civil, by Thomas Hobbes (University Press, 1904), p. xix. Originally published in 1651.
[T]here is a saying much usurped of late, That Wisedome is acquired, not by reading of Books, but of Men. Consequently whereunto, those persons, that for the most part can give no other proof of being wise, take great delight to shew what they think they have read in men, by uncharitable censures of one another behind their backs. But there is another saying not of late understood, by which they might learn truly to read one another, if they would take the pains; and that is, Nosce teipsum, Read thy self: which was not meant, as it is now used, to countenance, either the barbarous state of men in power, towards their inferiors ; or to encourage men of low degree, to a sawcie behaviour towards their betters; But to teach us, that for the similitude of the thoughts, and Passions of one man, to the thoughts, and Passions of another, whosoever looketh into himself, and considereth what he doth, when he does think, opine, reason, hope, feare, &c, and upon what grounds; he shall thereby read and know, what are the thoughts, and Passions of all other men, upon the like occasions.