So much for the physical equality. The moral equality is still less open to reasonable exception. By moral equality I understand, the propriety of applying one unalterable rule of justice to every case that may arise. This cannot be questioned, but upon arguments that would subvert the very nature of virtue. But surely justice is sufficiently intelligible in its own nature, abstractedly from the consideration whether it be or be not reduced into practice.
Justice has relation to beings endowed with perception, and capable of pleasure and pain.
Now it immediately results from the nature of such beings, independently of any arbitrary constitution, that pleasure is agreeable and pain odious, pleasure to be desired and pain to be disapproved. It is therefore just and reasonable that such beings should contribute, so far as it lies in their power, to the pleasure and benefit of each other. Among pleasures, some are more exquisite, more unalloyed and less precarious than others. It is just that these should be preferred. From these simple principles we may deduce the moral equality of mankind.