The system of Descartes... seemed to give a plausible reason for all those phenomena; and this reason seemed more just, as it is simple and intelligible to all capacities. But in philosophy, a student ought to doubt of the things he fancies he understands too easily, as much as of those he does not understand.
Theological religion is the source of all imaginable follies and disturbances. It is the parent of fanaticism and civil discord; it is the enemy of mankind.
It is the poverty connected with our species which subordinates one man to another. It is not inequality which is the real misfortune, it is dependence.
Descartes constructed as noble a road of science, from the point at which he found geometry to that to which he carried it, as Newton himself did after him. ... He carried this spirit of geometry and invention into optics, which under him became a completely new art.