Scanlon's dissertation and some of his first papers were in mathematical logic, where his main concern was in proof theory, but he turned to ethics and political philosophy, where he developed a version of contractualism in the line of John Rawls, Immanuel Kant, and Jean-Jacques Rousseau.

Contractualism is a constructivist attempt at providing a unified account of the subject matter of a central part of morality which Scanlon calls "what we owe to each other."

The normative domain of what we owe to each other is meant to encompass those duties to other people which we bear in virtue of their standing as rational creatures.

Scanlon grounds the reason-giving force of judgements about right and wrong in "the positive value of a way of living with others".

Rather, we tend to see reason to respect other human beings, to protect them from death and other forms of harm and, in general, to want their lives to go well.

Scanlon asserts that the proper response to the recognition of these distinctive features is to treat rational creatures in terms of principles which they could not reasonably reject.

The reason-giving force of moral judgements is grounded in an ideal of mutual recognition which requires treating others in accordance with principles that they could not reasonably reject.

Because mutual recognition requires that these other people are also appropriately motivated, this entails Scanlon's formulation of wrongness: "An act is wrong if and only if any principle that permitted it would be one that could reasonably be rejected by people moved to find principles for the general regulation of behaviour that others, similarly motivated, could not reasonably reject".

In turn, these values must accommodate the dictates of what we owe to each other to the extent that they involve relations with others, who have separate moral standing.

Scanlon's What We Owe to Each Other is referenced several times in the American comedy television series The Good Place, serving as one text used to instruct the protagonist Eleanor Shellstrop.