Mankind is a system of creatures, that continually need one another's assistance, without which they could not long subsist. It is therefore necessary, that everyone, according to his capacity and station, should contribute his part towards the good and preservation of the whole, and avoid whatever may be detrimental to it. For this end they are made capable of acquiring social or benevolent affections, (probably have the seeds of them implanted in their nature) with a moral sense or conscience, that approves of virtuous actions, and disapproves the contrary. This plainly shows them, that virtue is the law of their nature, and that it must be their duty to observe it, from whence arises moral obligation, tho' the sanctions of that law are unknown; for the consideration of what the event of an action may be to the agent, alters not at all the rule of his duty, which is fixed in the nature of things.
Catharine Trotter Cockburn, "Remarks upon some Writers in the Controversy concerning the Foundation of Moral Virtue and Moral Obligation", Philosophical Writings, Sheridan, ed. Broadview (Peterborough, ON: 2006) p. 114.