This line of reasoning also helps to explain why we recognize certain duties towards both men and animals, but certain others towards men only. For example, nobody would be thought to be oppressing animals because he did not allow them self-government; but, on the other hand, it is generally thought to be wrong to torture animals for fun. Now why is it that we do not acknowledge a duty to accord animals self-government? It is simply because we think that there is a real and relevant difference between men and animals in this respect. We can say 'If I were turned into an animal, I should stop having any desire for political liberty, and therefore the lack of it would be no hardship to me'. It is possible to say this even of men in certain stages of development. Nobody thinks that children ought to have complete political liberty; and most people recognize that it would be foolish to introduce the more advanced kinds of political liberty all at once in backward countries, where people have not got to the stage of wanting it, and would not know what to do with it if they got it. So this mode of reasoning allows us to make the many distinctions that are necessary in assessing our obligations towards different kinds of people, and indeed of sentient beings. In all cases the principle is the same—am I prepared to accept a maxim which would allow this to be done to me, were I in the position of this man or animal, and capable of having only the experiences, desires, &c., of him or it?
(R. M. Hare, Freedom and Reason [Oxford: Clarendon Press, 1963], 222-3 [italics in original])