Porphyry begins with an expression of surprise and regret at the apostasy of the Pythagorean renegade:—
“For when I reflect with myself upon the cause of your change of mind [so he addresses his former associate], I cannot believe, as the vulgar herd will suppose, that it has anything to do with reasons of health or strength, inasmuch as you yourself were used to assert that the fleshless diet is more consonant to healthfulness and to an even and proportionate endurance of philosophic toils (σύμμετρον ὑπομονὴν τῶν περὶ φιλοσοφίαν πόνων), and experience fully proved the truth of your conviction. Whether then it was through some other fallacy or delusion, or through a later notion that this or that diet makes no difference to the intellectual powers, or whether it was from the fear of incurring odium by opposition to orthodox customs, or what the reason may have been, I am unable to conjecture.”
He expresses his hope, or rather his belief, that, at least, the lapse was not due in this case to natural intemperance, or regret for the gluttonous habits (λαιμαργίας) of flesh-eating.
He then proceeds to quote and refute the fallacies of the ordinary systems and sects, and, in particular, the objections of one Clodius, a Neapolitan, who had published a treatise against Pythagoreanism. He professes that he does not hope to influence those who are engaged in sordid and selfish, or in sanguinary, pursuits. Rather he addresses himself to the man
“Who considers what he is, whence he came, and whither he ought to tend; and who, in what pertains to the nourishment of the body and other necessary concerns, is of really thoughtful and earnest mind—who resolves that he shall not be led astray and governed by his passions. And let such a man tell me whether a rich flesh diet is more easily procured, or incites less to the indulgence of irregular passions and appetites, than a light vegetable dietary. But if neither he, nor a physician, nor, indeed, any reasonable man whosoever, dares to affirm this, why do we persist in oppressing ourselves with gross feeding? And why do we not, together with that luxurious indulgence, throw off the encumbrances and snares which attend it?
“It is not from those who have lived on innocent foods that murderers, tyrants, robbers, and sycophants have come, but from eaters of flesh. The necessaries of life are few and easily procured, without violation of justice, liberty, or peace of mind; whereas luxury obliges those ordinary souls who take delight in it to covet riches, to give up their liberty, to sell justice, to misspend their time, to ruin their health, and to renounce the satisfaction of an upright conscience.”
In condemning animal sacrifice, he declares that “it is by means of an exalted and purified intellect alone that we can approximate to the Supreme Being, to whom nothing material should be offered.” He distinguishes four degrees of virtue, the lowest being that of the man who attempts to moderate his passions; the highest, the life of pure reason, by which man becomes one with the Supreme Existence.
In the third book, maintaining that other animals are endowed with high degrees of reasoning and of mental faculties, and, in some measure, even with moral perception, Porphyry proceeds logically to insist that they are, therefore, the proper objects of Justice:—
“By these arguments, and others which I shall afterwards adduce in recording the opinions of the old peoples, it is demonstrated that [many species of] the lower animals are rational. In very many, reason is imperfect indeed—of which, nevertheless, they are by no means destitute. Since then justice is due to rational beings, as our opponents allow, how is it possible to evade the admission also that we are bound to act justly towards the races of beings below us? We do not extend the obligations of justice to plants, because there appears in them no indication of reason; although, even in the case of these, while we eat the fruits we do not, with the fruits, cut away the trunks. We use corn and leguminous vegetables when they have fallen on the earth and are dead. But no one uses for food the flesh of dead animals, unless they have been killed by violence, so that there is in these things a radical injustice. As Plutarch says, it does not follow, because we are in need of many things, that we should therefore act unjustly towards all beings. Inanimate things we are allowed to injure to a certain extent, to procure the necessary means of existence—if to take anything from plants while they are growing can be said to be an injury—but to destroy living and conscious beings merely for luxury and pleasure is truly barbarous and unjust. And to refrain from killing them neither diminishes our sustenance nor hinders our living happily. If indeed the destruction of other animals and the eating of flesh were as requisite as air and water, plants and fruits, then there could be no injustice, as they would be necessary to our nature.”