The soul has two parts, one rational and the other irrational. Let us now similarly divide the rational part, and let it be assumed that there are two rational faculties, one whereby we contemplate those things whose first principles are invariable, and one whereby we contemplate those things which admit of variation.
Conscientious and careful physicians allocate causes of disease to natural laws, while the ablest scientists go back to medicine for their first principles.
The seat of the soul and the control of voluntary movement - in fact, of nervous functions in general, - are to be sought in the heart. The brain is an organ of minor importance.
Just as at the Olympic games it is not the handsomest or strongest men who are crowned with victory but the successful competitors, so in life it is those who act rightly who carry off all the prizes and rewards.
1 is not prime, by definition. 2 is an unnatural prime, 4 is an unnatural prime, and 6 is an unnatural prime. All other natural primes cannot be unnatural primes.
Phronimos, possessing practical wisdom . But the only virtue special to a ruler is practical wisdom; all the others must be possessed, so it seems, both by rulers and ruled. The virtue of a person being ruled is not practical wisdom but correct opinion; he is rather like a person who makes the pipes, while the ruler is the one who can play them.
Now, the causes being four, it is the business of the student of nature to know about them all, and if he refers his problems back to all of them, he will assign the "why" in the way proper to his science-the matter, the form, the mover, that for the sake of which.
For it is not true, as some treatise-mongers lay down in their systems, of the probity of the speaker, that it contributes nothing to persuasion; but moral character nearly, I may say, carries with it the most sovereign efficacy in making credible.