But to me all sciences seem vain and full of error that are not born of experience, mother of all certainty, and do not terminate in an actual experience.

To speak of this subject you must... explain the nature of the resistance of the air, in the second the anatomy of the bird and its wings, in the third the method of working the wings in their various movements, in the fourth the power of the wings and the tail when the wings are not being moved and when the wind is favourable to serve as guide in various movements.

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, but not with a corresponding degree of strength, though it is deficient only in the power of maintaining equilibrium. We may therefore say that such an instrument constructed by man is lacking in nothing except the life of the bird, and this life must needs be supplied from that of man.

The organ of perception acts more readily than judgment.

The noblest pleasure is the joy of understanding.

All our knowledge originates in opinion.

Realize that everything connects to everything else.