Bats … present a range of activity and a sensory apparatus so different from ours that the problem I want to pose is exceptionally vivid (though it c… - Thomas Nagel

I do not believe that the source of value is unitary — displaying apparent multiplicity only in its application to the world. I believe that value has fundamentally different kinds of sources, and that they are reflected in the classification of values into types. Not all values represent the pursuit of some single good in a variety of settings.

I believe that the general form of moral reasoning is to put yourself in other people's shoes. This leads to an impersonal concern for them corresponding to the impersonal concern for yourself that is needed to avoid a radical incongruity between your attitudes from the personal and impersonal standpoints, i.e. from inside and outside your life. Some considerable disparity remains, because your personal concern remains in relation to yourself and your life: they are not to be replaced or absorbed by the impersonal ones that correspond to them. (One is also typically concerned in a personal way for the interests of certain others to whom one is close.) But we derive moral reasons by forming in addition a parallel impersonal concern corresponding to the interests of all other individuals. It will be as strong or as weak, as comprehensive or as restricted, as the impersonal concern we are constrained by the pressures of congruency to feel about ourselves. In a sense, the requirement is that you love your neighbor as yourself; but only as much as you love yourself when you look at yourself from outside, with fair detachment.

Even if I could by gradual degrees be transformed into a bat, nothing in my present constitution enables me to imagine what the experiences of such a future stage of myself thus metamorphosed would be like. The best evidence would come from the experience of bats, if we only knew what they were like.