To understand this for sense it is not required that a man should be a geometrician or a logician, but that he should be mad.
["This" is that the volume generated by revolving the region under 1/x from 1 to infinity has finite volume.]
Quoted in N Rose Mathematical Maxims and Minims (Raleigh N C 1988).
The errors of definitions multiply themselves according as the reckoning proceeds; and lead men into absurdities, which at last they see but cannot avoid, without reckoning anew from the beginning.
Quoted in J R Newman, The World of Mathematics (New York 1956).
A quotation about Thomas Hobbes by John Aubrey (1626-1697)
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", sayd 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 trueth. This made him in love with geometry.
Quoted in O L Dick, Brief Lives (Oxford 1960)
[a quotation by John Aubrey]
I have heard Mr Hobbes say that he was wont to draw lines on his thigh and on his sheets, abed and also multiply and divide.
Quoted in D MacHale, Comic Sections (Dublin 1993)
Nature itself cannot err
Geometry (which is the only science that it hath pleased God to bestow on mankind) ...
Words are wise men's counters, they do but reckon by them: but they are the money of fools, that value them by the authority of an Aristotle, a Cicero, or a Thomas, or any other doctor whatsoever, if but a man.
I have read little. If I had read as much as other men had, I would have known as little.
Quoted in Des MacHale, Wisdom (London, 2002).