First Proposition.

All the capacities implanted in a Creature by nature, are destined to unfold themselves, completely and conformably to their End, in the course of time.

This Proposition is established by Observation, external as well as internal or anatomical, in the case of all animals. An organ which is not to be used, or an arrangement which does not attain its End, is a contradiction in the teleological science of Nature. For, if we turn away from that fundamental principle, we have then before us a Nature moving without a purpose, and no longer conformable to law; and the cheerless gloom of chance takes the place of the guiding light of Reason.