Every faculty in one man is the measure by which he judges of the the like faculty in another. I judge of your sight by my sight, of your ear by my ear, of your reason by my reason, of your resentment by my resentment, of your love by my love. I neither have, nor can have, any other way of judging about them.

– Adam Smith

Smith, Adam. The Theory of Moral Sentiments. United Kingdom, Penguin Publishing Group, 2010.