And what are these fluxions? The velocities of evanescent increments? They are neither finite quantities, nor quantities infinitely small, nor yet nothing. May we not call them ghosts of departed quantities?
The method of Fluxions is the general key by help whereof the modern mathematicians unlock the secrets of Geometry, and consequently of Nature.
Quoted in E T Bell, Men of Mathematics
Of late the speculations about Infinities have run so high, and grown to such strange notions, as have occasioned no small scruples and disputes among the geometers of the present age. Some there are of great note who, not contented with holding that finite lines may be divided into an infinite number of parts, do yet further maintain that each of these infinitesimals is itself subdivisible into an infinity of other parts or infinitesimals of a second order, and so on ad infinitum. These I say assert there are infinitesimals of infinitesimals, etc., without ever coming to an end; so that according to them an inch does not barely contain an infinite number of parts, but an infinity of an infinity of an infinity ad infinitum of parts.
The Principles of Human Knowledge
The table I write on I say exists ... meaning thereby that if I was in my study I might perceive it, or that some other spirit actually does perceive it.
It is impossible that a man who is false to his friends and neighbours should be true to the public.
Quoted in Des MacHale, Wisdom (London, 2002).
Esse est percipi. To be is to be perceived.