There is nothing which deceives us as much as our own judgement.
The greatest deception which men incur proceeds from their opinions.
Avoid the precepts of those thinkers whose reasoning is not confirmed by experience.
Man discourseth greatly, and his discourse is for the greater part empty and false; the discourse of animals is small, but useful and true: slender certainty is better than portentous falsehood.
What is an element? It is not in man's power to define the quiddity of the elements, but a great many of their effects are known.
That which is divisible in fact is divisible in potentiality also; but not all quantities which are divisible in potentiality are divisible in fact.
What is that thing which is not defined and would { 16} not exist if it were defined? It is infinity, which if it could be defined would be limited and finite, because that which can be defined ends with the limits of its circumference, and that which cannot be defined has no limits.
O contemplators of things, do not pride yourselves for knowing those things which nature by herself and her ordination naturally conduces; but rejoice in knowing the purposes of those things which are determined by your mind.
Consider, O reader, how far we can lend credence to the ancients who strove to define the soul and life,--things which cannot be proved; while those things which can be clearly known and proved by experience remained during so many centuries ignored and misrepresented! The eye, which so clearly demonstrates its functions, has been up to my time defined in one manner by countless authorities; I by experience have discovered another definition.
[Sidenote: Beauty of Nature's Inventions]
Although human ingenuity may devise various inventions which, by the help of various instruments, answer to one and the same purpose, yet { 17} will it never discover any inventions more beautiful, more simple or more practical than those of nature, because in her inventions there is nothing lacking and nothing superfluous; and she makes use of no counterpoise when she constructs the limbs of animals in such a way as to correspond to the motion of their bodies, but she puts into them the soul of the body. This is not the proper place for this discourse, which belongs rather to the subject of the composition of animated bodies; and the rest of the definition of the soul I leave to the minds of the friars, the fathers of the people, who know all secrets by inspiration. I leave the sacred books alone, because they are the supreme truth.