T 2.3.6.8

But eloquence is not always necessary. The bare opinion of another, especially when inforc'd with passion, will cause an idea of good or evil to have an influence upon us, which wou'd otherwise have been entirely neglected. This proceeds from the principle of sympathy or communication; and sympathy, as I have already observ'd, is nothing but the conversion of an idea into an impression by the force of imagination.