Every obstacle is destroyed through rigor.

We must doubt the certainty of everything which passes through the senses, but how much more ought we to doubt things contrary to the senses, such as the existence of God and the soul.

average human “looks without seeing, listens without hearing, touches without feeling, eats without tasting, moves without physical awareness, inhales without awareness of odour or fragrance, and talks without thinking.

I roamed the countryside searching for answers to things I did not understand. Why shells existed on the tops of mountains. How the various circles of water form around the spot which has been struck by a stone, and why a bird sustains itself in the air.

You don't get into trouble because of the things you don't know. It is the things you don't know you don't know that really get you into a mess.

Nature never breaks her own laws.

The young man should first learn perspective, then the proportions of objects. Next, copy work after the hand of a good master, to gain the habit of drawing parts of the body well; and then to work from nature, to confirm the lessons learned.