Neither Aquinas nor Kant nor Newman denied, however, that animals could suffer: Descartes and Malebranche thought differently. It is impossible, they argued, to be cruel to animals, since animals are incapable of feeling. They lack not only—as Aquinas had followed Aristotle in arguing—a rational soul but even that sensitive soul which both Aristotle and Aquinas had allowed them. To suppose that animals could feel would be to suggest that there could be pain and suffering where there has been no sin. For animals did not eat of the Forbidden Tree. "Being innocent," Malebranche writes, "if they were capable of feeling, the effect would be that under the government of an infinitely just and all-powerful God an innocent creature would suffer pain, which is a penalty, and the punishment of some sin." The only possible conclusion, appearances to the contrary notwithstanding, is that animals cannot feel. "They eat without pleasure," Malebranche therefore tells us, "they cry without sorrow . . . , they desire nothing, they fear nothing, they know nothing." (The Stoic Chrysippus, it is worth noting, had also suggested that animals do not feel but only "as it were" feel.) What we hear as a cry of pain is of no more significance than the creaking of a machine. An organ, the Cartesian Rouhault argues, makes more noise when I play it than an animal when it cries out, yet we do not ascribe feelings to the organ.
These teachings, it should be observed, were more than metaphysical speculations. They had a direct effect on seventeenth-century behavior as manifested, for example, in the popularity of public vivisections, not as an aid to scientific discovery but simply as a technical display. "They administered beatings to dogs with perfect indifference," so La Fontaine, a contemporary observer, tells us, "and made fun of those who pitied the creatures as if they had felt pain. . . . They nailed poor animals up on boards by their four paws to vivisect them and see the circulation of the blood which was a great subject of conversation."
(John Passmore, "The Treatment of Animals," Journal of the History of Ideas 36 [April-June 1975]: 195-218, at 204 [italics in original; footnotes omitted])