Pathocentrism

Since the good is pleasure and the evil suffering, what grants moral standing can be neither reason nor speech but the capacity to suffer alone: every being with an interest in its pain ceasing counts in the calculus. Bentham draws from this criterion a consequence that rationalist moralities refused, the inclusion of animals; Singer reads it as the principle of equal consideration of interests and denounces speciesism as a prejudice of the same structure as racism. The moral circle thus widens to all sentient life, by internal consistency rather than by sentiment.

Bentham, An Introduction to the Principles of Morals and Legislation, chapter 17 · Singer, Animal Liberation

Non-harming (ahiṃsā) and the first precept extend moral consideration to all sentient beings capable of suffering, not to humans alone. Compassion expressly takes in the whole of living beings caught in the cycle of rebirth, which places Buddhism on the pathocentric side.

Karaṇīya Mettā Sutta (the discourse on loving-kindness) · Dhammapada, ch. X (Violence)

If the sole title to enter the calculus is to be able to feel pleasure and pain, then the boundary of moral consideration must follow sentience, not reason or language. Bentham thus turns back both the Cartesian argument of the animal-machine and the one that once excluded the slave: it is not the faculty of reasoning or talking that grounds a claim to consideration, but the capacity to suffer. The conclusion follows from the consistency of the utilitarian criterion itself: consideration extends to every sentient being, placing him in pathocentrism and making him a precursor of the animal cause.

An Introduction to the Principles of Morals and Legislation, ch. XVII, §1, footnote (the suffering of animals)

Non-harming (ahiṃsā) and the first precept, to abstain from harming the living, extend moral consideration to all sentient beings capable of suffering, not to humans alone. All fear the rod, all hold life dear: compassion expressly takes in the whole of living beings caught in the cycle of rebirth, which places the teaching on the pathocentric side.

Dhammapada, ch. X (Violence), 129-130 · Karaṇīya Mettā Sutta, Sutta Nipāta 1.8 (may all beings be happy)

Since the moral criterion is pleasure and pain, the circle of moral concern extends to all sentient beings capable of suffering, not to humans alone: a pathocentrism. Mill explicitly counts the happiness of animals in the utilitarian calculus and supports early legislation against cruelty toward them.

Utilitarianism, ch. 2 (the happiness of all sentient creatures) · Whewell on Moral Philosophy (1852), on the moral standing of animals

The moral circle extends to everything that suffers: animals, manifestations of the same will as ourselves, are the direct object of compassion, and he reproaches Christianity and Kant alike for having made beasts into mere things for our use, a doctrine he finds 'revolting and abominable.' The moral boundary runs at sentience, not at reason; the background stays metaphysical, the same will throughout nature, which lends it a biocentric tinge.

On the Basis of Morality, §19

Against the pride that sets man atop creation, Montaigne brings the beasts near to us: "when I play with my cat, who knows whether she is not amusing herself with me more than I with her?". They have their intelligence, their affections, a communication. From this kinship he draws a duty: we owe "justice" to human beings, but "grace and kindness" to the other creatures, and cruelty toward animals fills him with horror. Moral consideration thus spills beyond humanity toward whatever can suffer, without going so far as an equality of all living things.

Essays, II, 12, "Apology for Raymond Sebond" and II, 11, "Of Cruelty"