Hobbes, Thomas. 1588-1679. English philosopher

"And therefore in geometry (which is the only science that it hath pleased God hitherto to bestow on mankind), men begin at settling the significations of their words; which settling of significations, they call definitions, and place them in the beginning of their reckoning."
Leviathan 1651, Chapter IV, Of Speech.

Hobbes and the Foundations of Knowledge: Geometry, Definitions, and Reason

"For there is not one of them that begins his ratiocination from the definitions or explications of the names they are to use; which is a method that hath been used only in geometry, whose conclusions have thereby been made indisputable................ . For who is so stupid as both to mistake in geometry, and also to persist in it, when another detects his error to him?"
Leviathan 1651. Chapter V, Of Reason and Science.



"For I doubt not, but if it had been a thing contrary to any man's right of dominion, or to the interest of men that have dominion, that the three angles of a triangle should be equal to two angles of a square, that doctrine should have been, if not disputed, yet by the burning of all books of geometry suppressed, as far as he whom it concerned was able."
Leviathan 1651. Chapter XI, Of the Difference of Manners.



Aubrey, John. 1626-1697. English antiquarian. About Thomas Hobbes:
He was 40 years old before he looked on geometry; which happened accidentally. Being in a gentleman's library, Euclid's Elements lay open, and "twas the 47 El. libri I" [Pythagoras' Theorem]. He read the proposition "By God", said he, "this is impossible:" So he reads the demonstration of it, which referred him back to such a proposition; which proposition he read. That referred him back to another, which he also read. Et sic deinceps, that at last he was demonstratively convinced of that truth. This made him in love with geometry.
In O. L. Dick (ed.) Brief Lives, Oxford: Oxford University Press, 1960.