This particular action is like certain other actions, or belongs to a class of actions, which we habitually regard as right or wrong, and, consequently, as soon as the reference or association is made, the moral feeling supervenes.

" As nimbly as a sea-gull runs upon the sand, the young creature flew across the now level raft toward the sea, but a strong hand clutched her as she was about to step overboard, and compelled her back to her place on the platform, where, bound with cords, she lay raving, until sleep or unconsciousness mercifully supervened to spare me the spectacle of her agony, which no human power could alleviate.

Since the will is the primary and radical element in human nature, and intellect merely supervenes as something secondary, people are more likely to believe that the opinion you express with so much vehemence is due to the excited state of your will, rather than that the excitement of the will comes only from the ardent nature of your opinion.