If we apply the criterion of duty, the question of whether animals have rights can be readily answered: we have merely to ask whether, in considering an action affecting an animal, we could assent to such an action after abstracting from numerical determination. In other words, we have to ask whether we would consent to be used as mere means by another being far superior to us in strength and intelligence. This question answers itself. The fact that man has other beings in his power, and that he is in a position to use them as means to his own ends, is purely fortuitous.
(Leonard Nelson, System of Ethics, trans. Norbert Guterman [New Haven: Yale University Press, 1956], 141 [first published in German in 1932])