A bird is an instrument working according to mathematical law, which instrument it is within the capacity of man to reproduce with all its movements.

Just as eating against one's will is injurious to health, so studying without a liking for it spoils the memory, and it retains nothing it takes in.

It is useful to constantly observe, note, and consider.

As regards this vice, we read that the peacock is more guilty of it than any other animal. For it is always contemplating the beauty of its tail, which it spreads in the form of a wheel, and by its cries attracts to itself the gaze of the creatures that surround it. And this is the last vice to be conquered.

All our knowledge hast its origins in our perceptions … In nature there is no effect without a cause … Experience never errs; it is only your judgments that err by promising themselves effects such as are not caused by your experiments … Science is the observation of things possible, whether present or past; prescience is the knowledge of things which may come to pass.

Blinding ignorance does mislead us. O! Wretched mortals, open your eyes!

We know more about the movement of celestial bodies than about the soil underfoot.