Justification to other people › Why the comparison includes alternatives

Any principle can impose burdens. A rule permitting one person to cancel an assurance may burden the person relying on it. A rule requiring performance may burden the person who gave it. Asking only whether a principle has costs would leave us unable to choose anything. Scanlon instead considers objections in light of the alternatives and the burdens those alternatives would impose.

In the lift example, the friend loses the assurance around which they planned. The promiser gives up a more enjoyable evening. Those descriptions start the comparison, but they do not finish it. The seriousness of the reliance, the nature of the assurance and the costs of keeping it all matter to a defensible judgment.

Change the circumstances and the reasons can change. If the promiser needs to respond to an emergency, a principle requiring performance without exceptions would impose a different burden. The friend's original expectation still matters, but it need not settle the result. Contractualist reasoning asks what qualifications each side could reasonably require.

This is a structure for moral assessment, not a single numerical measure of complaints. Calling one objection stronger requires a substantive judgment about the reasons involved. The theory cannot avoid that judgment by assigning an arbitrary score to each person and selecting the largest number. Precision about the comparison is more useful than the appearance of a calculation.