Ele era um leitor constante da literatura filosófica britânica, assim como de sua poesia e até mesmo dos jornais ingleses. Foi por meio da leitura diária do Times e do Birmingham Journal que ele manteve-se atualizado em relação aos progressos que essa nação fazia neste tópico jurídiro e moral.
A literatura inglesa também o influenciou em relação ao interesse nascente pela cultura oriental, nomeadamente da hindu e da chinesa. Nesta área, os alemães estavam menos atrasados, com grandes estudos por parte de Schlegel. No entanto, no que diz respeito especificamente à importância que os hindus prestam aos animais em sua moral e direito, a Inglaterra estava adiantada. E isto refletiu-se na consciência, pioneira dentro do pensamento e políticas europeus na modernidade, em relação à necessidade de lutar por um alargamento da esfera moral tradicional. Um exemplo disso foi registrado pelo próprio Schopenhauer, que cita alguns casos nos quais animais humanos foram punidos legalmente por mal-tratos infligidos a cães e cavalos. Schopenhauer aplaudia com grande entusiasmo essas decisões da lei britânica.
Caricatura de Schopenhauer com seus poodles. Na verdade, numa alusão à teoria da transmigração, ele dava o mesmo nome aos sucessivos cães poodle que ele manteve durante sua vida. Como curiosidade, cito um divertido texto sobre pessoas destacadas (entre elas, Victor Hugor, Luís XIV, Tolstoy e o próprio Schopenhauer) que tiveram, como animal doméstico, poodles.
Para ilustrar a defesa de Schopenhauer, cito dois trechos de sua obra que são emblemáticos. Pretendo comentá-los logo, assim como disponibilizar a tradução. Por hora, a versão em língua inglesa, tão importante para o filósofo neste ponto.
I may mention here another fundamental error of Christianity, an error which cannot be explained away, and the mischievous consequences of which are obvious every day: I mean the unnatural distinction Christianity makes between man and the animal world to which he really belongs. It sets up man as all-important, and looks upon animals as merely things. Brahmanism and Buddhism, on the other hand, true to the facts, recognize in a positive way that man is related generally to the whole of nature, and specially and principally to animal nature; and in their systems man is always represented by the theory of metempsychosis and otherwise, as closely connected with the animal world. The important part played by animals all through Buddhism and Brahmanism, compared with the total disregard of them in Judaism and Christianity, puts an end to any question as to which system is nearer perfection, however much we in Europe may have become accustomed to the absurdity of the claim. Christianity contains, in fact, a great and essential imperfection in limiting its precepts to man, and in refusing rights to the entire animal world. As religion fails to protect animals against the rough, unfeeling and often more than bestial multitude, the duty falls to the police; and as the police are unequal to the task, societies for the protection of animals are now formed all over Europe and America. In the whole of uncircumcised Asia, such a procedure would be the most superfluous thing in the world, because animals are there sufficiently protected by religion, which even makes them objects of charity. How such charitable feelings bear fruit may be seen, to take an example, in the great hospital for animals at Surat, whither Christians, Mohammedans and Jews can send their sick beasts, which, if cured, are very rightly not restored to their owners. In the same way when a Brahman or a Buddhist has a slice of good luck, a happy issue in any affair, instead of mumbling a Te Deum, he goes to the market-place and buys birds and opens their cages at the city gate; a thing which may be frequently seen in Astrachan, where the adherents of every religion meet together: and so on in a hundred similar ways. On the other hand, look at the revolting ruffianism with which our Christian public treats its animals; killing them for no object at all, and laughing over it, or mutilating or torturing them: even its horses, who form its most direct means of livelihood, are strained to the utmost in their old age, and the last strength worked out of their poor bones until they succumb at last under the whip. One might say with truth, Mankind are the devils of the earth, and the animals the souls they torment. But what can you expect from the masses, when there are men of education, zoologists even, who, instead of admitting what is so familiar to them, the essential identity of man and animal, are bigoted and stupid enough to offer a zealous opposition to their honest and rational colleagues, when they class man under the proper head as an animal, or demonstrate the resemblance between him and the chimpanzee or ourang-outang. It is a revolting thing that a writer who is so pious and Christian in his sentiments as Jung Stilling should use a simile like this, in his Scenen aus dem Geisterreich. (Bk. II. sc. i., p. 15.) “Suddenly the skeleton shriveled up into an indescribably hideous and dwarf-like form, just as when you bring a large spider into the focus of a burning glass, and watch the purulent blood hiss and bubble in the heat.” This man of God then was guilty of such infamy! or looked on quietly when another was committing it! in either case it comes to the same thing here. So little harm did he think of it that he tells us of it in passing, and without a trace of emotion. Such are the effects of the first chapter of Genesis, and, in fact, of the whole of the Jewish conception of nature. The standard recognized by the Hindus and Buddhists is the Mahavakya (the great word),—“tat-twam-asi” (this is thyself), which may always be spoken of every animal, to keep us in mind of the identity of his inmost being with ours. Perfection of morality, indeed! Nonsense.
(O sistema cristão; Religião, um diálogo e outros ensaios; in Parerga e Paralipomena)
Boundless compassion for all living beings is the firmest and surest guarantee of pure moral conduct, and needs no casuistry. Whoever is inspired with it will assuredly injure no one, will wrong no one, will encroach on no one's rights; on the contrary, he will be lenient and patient with everyone, will forgive everyone, will help everyone as much as he cares, and all his actions will bear the stamp of justice, philanthropy, and Wing-kindness. On the other hand, if we attempt to say, "This man is virtuous but knows no compassion," or, "He is an unjust and malicious man yet he is very compassionate," the contradiction is obvious. Tastes differ, but I know of no finer prayer than the one which ends old Indian dramas (just as in former times English plays ended with a prayer for the King). It runs: "May all living beings remain free from pain." . . .
The moral incentive advanced by me as the genuine, is further confirmed by the fact that the animals are also taken under its protection. In other European systems of morality they are badly provided for, which is most inexcusable. They are said to have no rights, and there is the erroneous idea that our behavior to them is without moral significance, or, as it is said in the language of that morality, there are no duties to animals. All this is revoltingly crude, a barbarism of the West, the source of which is to be found in Judaism. In philosophy it rests, despite all evidence to the contrary, on the assumed total difference between man and animal. We all know that such difference was expressed most definitely and strikingly by Descartes as a necessary consequence of his errors. Thus when the philosophy of Descartes, Leibniz, and Wolff built up rational psychology out of abstract concepts and constructed an immortal anima rationales, the natural claims of the animal world obviously stood up against this exclusive privilege, this patent of immortality of the human species, and nature, as always on such occasions, entered her silent protest. With an uneasy intellectual conscience, the philosophers then had to try to support rational psychology by means of the empirical. They were therefore concerned to open up a vast chasm, an immeasurable gulf between man and animal in order to represent them as fundamentally different, in spite of all evidence to the contrary. ... In the end animals would be quite incapable of distinguishing themselves from the external world and would have no consciousness of themselves, no ego! To answer such absurd statements, we can point simply to the boundless egoism inherent in every animal, even the smallest and lowest, which shows clearly enough how very conscious they are of their ego in face of the world or the non-ego. If any Cartesian were to find himself clawed by a tiger, he would become aware in the clearest possible manner of the sharp distinction such a beast draws between its ego and the non-ego. In keeping with such sophisms of philosophers, we find a popular peculiarity in many languages, especially German, of giving animals special words of their own for eating, drinking, pregnancy, parturition, dying, and their bodies, so that we need not use the same words which describe those acts among human beings: and thus we conceal under a diversity or words the perfect and complete identity of the thing. Since the ancient languages did not recognize any such duplication, but rather frankly and openly denoted the same thing by the same word, that miserable artifice is undoubtedly the work of European priests and parsons. In their profanity these men think they cannot go far enough in disavowing and reviling the eternal essence that lives in all animals, and thus have laid the foundation of that harshness and cruelty to animals which is customary in Europe, but which no native of the Asiatic uplands can look at without righteous horror. In the English language we do not meet with this contemptible trick, doubtless because the Saxons, when they conquered England, were not yet Christians. On the other hand, we do find an analogy to it in the strange fact that in English all animals are of the neuter gender and so are represented by the pronoun "it," just as if they were inanimate things. The effect of this artifice is quite revolting, especially in the case of primates, such as dogs, monkeys, and the like; it is unmistakably a priestly trick for the purpose of reducing animals to the level of things. The ancient Egyptians, whose whole life was dedicated to religious purposes, put the mummies of the ibis, crocodile, and so on, in the same vault with those of human beings. In Europe, however, it is an abomination and a crime for a faithful dog to be buried beside the resting place of his master, though at times, from a faithfulness and attachment not to be found among the human race, he there awaited his own death. Nothing leads more definitely to a recognition of the identity of the essential nature in animal and human phenomena than a study of zoology and anatomy. What, then, are we to say when in these days  a bigoted and canting zootomist has the audacity to emphasize an absolute and radical difference between man and animal, and goes so far as to attack and disparage honest zoologists who keep aloof from all priestly guile, toadyism, and hypocrisy, and pursue their course under the guidance of nature and truth? One must be really quite blind or totally chloroformed by the factor Judaicus not to recognize that the essential or principal thing in the animal and man is the same, and that what distinguishes the one from the other is not to be found in the primary and original principle, in the archaeus, in the inner nature, in the kernel of the two phenomena, such kernel being in both alike the will of the individual; but only in the secondary, in the intellect, in the degree of the cognitive faculty. In man this degree is incomparably higher through the addition of the faculty of abstract knowledge, called reason. Yet this superiority is traceable only to a greater cerebral development, and hence to the somatic difference of a single part, the brain, and in particular, its quantity. On the other hand, the similarity between animal and man is incomparably greater, both psychically and somatically. And so we must remind the Western, Judaized despiser of animals and idolater of the faculty of reason that, just as he was suckled by his mother, so too was the dog by his. Even Kant fell into this mistake of his contemporaries and countrymen; this I have already censured. The morality of Christianity has no consideration for animals, a defect that is better admitted than perpetuated. . . .
Since compassion for animals is so intimately associated with goodness of character, it may be confidently asserted that whoever is cruel to animals cannot be a good man. This compassion also appears to have sprung from the same source as the virtue that is shown to human beings has. Thus, for example, persons of delicate feelings, on realizing that in a bad mood, in anger, or under the influence of wine, they unnecessarily or excessively, or beyond propriety, ill-treated their dog, horse, or monkey—these people will feel the same remorse, the same dissatisfaction with themselves as is felt when they recall a wrong done to human beings, where it is called the voice of reproving conscience.
(Confirmação do fundamento da moral que foi apresentado; parte 7; in: Sobre o fundamento da moral).