John MacFarlane, "Relativism and Disagreement"

Contexualists (someone who thinks the content of a proposition is partly determined by the context of utterance) can account for the intuition that disagreements of taste are sometimes not genuine disagreements, but they can't account for the intuition that sometimes disagreements of taste are genuine disagreements. Relativists can account for both intuitions by taking disagreement to be when one party to the disagreement accepts a proposition and the other rejects it, and relative to the "circumstance of evaluation that is relevant to the assessment of the acceptance (rejection) [of the proposition] in its context" both parties can't be right. So, when there is genuine disagreement, both parties share the circumstance of evaluation relevant to the assessment of the proposition, and when disagreement is merely apparent, the parties don't share that circumstance of evaluation.