Natural conscience consists in these two things.
1. In that disposition to approve or disapprove the moral treatment which passes between us and others, from a determination of the mind to be easy or uneasy, in a consciousness of our being consistent or inconsistent with ourselves. Hereby we have a disposition to approve our own treatment of another, when we are conscious to ourselves that we treat him so as we should expect to be treated by him, were he in our case and we in his; and to disapprove of our own treatment of another, when we are conscious that we should be displeased with the like treatment from him, if we were in his case. So we in our consciences approve of another’s treatment of us, if we are conscious to ourselves, that if we were in his case, and he in ours, we should think it just to treat him as he treats us; and disapprove his treatment of us, when we are conscious that we should think it unjust, if we were in his case. Thus men’s consciences approve or disapprove the sentence of their judge, by which they are acquitted or condemned. But this is not all ... there is another thing that must precede it, and be the foundation of it. ...
2. The other thing which belongs to the approbation or disapprobation of natural conscience, is the sense of desert ... consisting ... in a natural agreement, proportion, and harmony, between malevolence or injury, and resentment and punishment; or between loving and being loved, between showing kindness and being rewarded, &c. Both these kinds of approving or disapproving, concur in the approbation or disapprobation of conscience: the one founded on the other. Thus, when a man’s conscience disapproves of his treatment of his neighbour, in the first place, he is conscious, that if he were in his neighbour’s stead, he should resent such treatment from a sense of justice, or from a sense of uniformity and equality between such treatment, and resentment, and punishment ... And then, in the next place, he perceives, that therefore he is not consistent with himself, in doing what he himself should resent in that case; and hence disapproves it, as being naturally averse to opposition to himself.
Dissertation on the nature of true virtue Chapter 5