Every action needs to be prompted by a motive.
Each man is always in the middle of the surface of the earth and under the zenith of his own hemisphere, and over the centre of the earth.
Drawing is based upon perspective, which is nothing else than a thorough knowledge of the function of the eye.
Constancy does not begin, but is that which perseveres.
Blinding ignorance does mislead us… O! Wretched mortals, open your eyes!
Beyond a doubt truth bears the same relation to falsehood as light to darkness.
Any one who in discussion relies upon authority uses, not his understanding, but rather his memory.
All our knowledge has its origin in our perceptions.
All knowledge which ends in words will die as quickly as it came to life, with the exception of the written word: which is its mechanical part.
A point is not part of a line.