The philosophical systems, in spite of their number and variety, may be reduced to three: (1) the Materialists; (2) the Naturalists; (3) the Theists.
(1) The Materialists. They reject an intelligent and omnipotent Creator and disposer of the universe. In their view the world exists from all eternity and had no author. The animal comes from semen and semen from the animal; so it had always been and will always be; those who maintain this doctrine are atheists.
(2) The Naturalists. These devote themselves to the study of nature and of the marvelous phenomena of the animal and vegetable world. Having carefully analyzed animal organs with the help of anatomy, struck with the wonders of God's work and with the wisdom therein revealed, they are forced to admit the existence of a wise Creator who knows the end and purpose of everything. And certainly no one can study anatomy and the wonderful mechanism of living things without being obliged to confess the profound wisdom of him who has framed the bodies of animals and especially of man. But carried away by their natural researches they believed that the existence of a being absolutely depended upon the proper equilibrium of its organism. According to them, as the latter perishes and is destroyed, so is the thinking faculty which is bound up with it; and as they assert that the restoration of a thing once destroyed to existence is unthinkable, they deny the immortality of the soul. Consequently they deny heaven, hell, resurrection, and judgment. Acknowledging neither a recompense for good deeds nor a punishment for evil ones, they fling off all authority and plunge into sensual pleasures with the avidity of brutes. These also ought to be called atheists, for the true faith depends not only on the acknowledgment of God, but of his Apostle and of the day of judgment. And although they acknowledge God and his attributes, they deny a judgment to come.
(3) Next come the Theists. Among them should be reckoned Socrates, who was the teacher of Plato as Plato was of Aristotle. This latter drew up for his disciples the rules of logic, organized the sciences, elucidated what was formerly obscure, and expounded what had not been understood. This school refuted the systems of the two others, i.e., the Materialists and Naturalists; but in exposing their mistaken and perverse beliefs, they made use of arguments which they should not. "God suffices to protect the faithful in war" (Koran, xxxiii. 25).
Aristotle also contended with success against the theories of Plato, Socrates, and the theists who had preceded him, and separated himself entirely from them; but he could not eliminate from his doctrine the stains of infidelity and heresy which disfigure the teaching of his predecessors. We should therefore consider them all as unbelievers, as well as the so-called Mussulman philosophers, such as Ibn Sina (Avicenna) and Farabi, who have adopted their systems.
Let us, however, acknowledge that among Mussulman philosophers none has better interpreted the doctrine of Aristotle than the latter. What others have handed down as his teaching is full of error, confusion, and obscurity adapted to disconcert the reader. The unintelligible can neither be accepted nor rejected. The philosophy of Aristotle, all serious knowledge of which we owe to the translation of these two learned men, may be divided into three portions: the first contains matter justly chargeable with impiety, the second is tainted with heresy, and the third we are obliged to reject absolutely. We proceed to details:
Divisions of the Philosophic Sciences
These sciences, in relation to the aim we have set before us, may be divided into six sections: (1) Mathematics; (2) Logic; (3) Physics; (4) Metaphysics; (5) Politics; (6) Moral Philosophy.
(1) Mathematics. Mathematics comprises the knowledge of calculation, geometry, and cosmography: it has no connection with the religious sciences, and proves nothing for or against religion; it rests on a foundation of proofs which, once known and understood, can not be refuted. Mathematics tend, however, to produce two bad results.
The first is this: Whoever studies this science admires the subtlety and clearness of its proofs. His confidence in philosophy increases, and he thinks that all its departments are capable of the same clearness and solidity of proof as mathematics. But when he hears people speak of the unbelief and impiety of mathematicians, of their professed disregard for the Divine Law, which is notorious, it is true that, out of regard for authority, he echoes these accusations, but he says to himself at the same time that, if there was truth in religion, it would not have escaped those who have displayed so much keenness of intellect in the study of mathematics.