Aristotle's Logic.
Aristotle's logic—his art of reasoning—is so much the more to be esteemed as he had to deal with the Greeks, who were continually holding captious arguments, from which fault his master Plato was even less exempt than others.
Take, for example, the article by which, in the "Phædon" Plato proves the immortality of the soul:
"Do you not say that death is the opposite of life? Yes. And that they spring from each other? Yes. What, then, is it that springs from the living? The dead. And what from the dead? The living. It is, then, from the dead that all living creatures arise. Consequently, souls exist after death in the infernal regions."
Sure and unerring rules were wanted to unravel this extraordinary nonsense, which, through Plato's reputation, fascinated the minds of men. It was necessary to show that Plato gave a loose meaning to all his words.
Death does not spring from life, but the living man ceases to live. The living springs not from the dead, but from a living man who subsequently dies. Consequently, the conclusion that all living things spring from dead ones is ridiculous.
From this conclusion you draw another, which is no way included in the premises, that souls are in the infernal regions after death. It should first have been proved that dead bodies are in the infernal regions, and that the souls accompany them.
There is not a correct word in your argument. You should have said—That which thinks has no parts; that which has no parts is indestructible: therefore, the thinking faculty in us, having no parts, is indestructible. Or—the body dies because it is divisible; the soul is indivisible; therefore it does not die. Then you would at least have been understood.
It is the same with all the captious reasonings of the Greeks. A master taught rhetoric to his disciple on condition that he should pay him after the first cause that he gained. The disciple intended never to pay him. He commenced an action against his master, saying: "I will never pay you anything, for, if I lose my cause I was not to pay you until I had gained it, and if I gain it my demand is that I may not pay you."
The master retorted, saying: "If you lose you must pay; if you gain you must also pay; for our bargain is that you shall pay me after the first cause that you have gained."