5 ideas
Twain recalls a young enslaved man named Jerry who preached satirical sermons from atop a woodpile, with one core text: 'You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.' The joke carries the whole thesis: a person's livelihood (the source of their bread) predicts their stated beliefs better than any argument they could offer.
Twain widens Jerry's point beyond money: the deeper corn-pone is social approval, the need to be well regarded by one's neighbors and one's group. A person will give up comfort, and even argue against their own interest, to avoid the pain of standing apart and being disapproved of.
Twain treats the way hoopskirts and other fashions spread and vanish as the template for how political, moral, and religious views move through a population. People adopt a new style because the group adopts it, then find reasons it is sensible. Viewed this way, sudden shifts in collective belief look like wardrobe changes, not intellectual discoveries.
Twain argues that a person cannot approve of himself unless others approve of him first, so inner conviction is borrowed from outer endorsement. This is why conformity feels like integrity from the inside: the group's verdict has been absorbed as one's own conscience.
Most opinions are formed by feeling and by the pull of the crowd, then dressed afterward in reasons that make them look independently thought out. Twain says genuine independent reasoning on large public questions is rare. What people call their 'convictions' is usually group sentiment they have inherited, plus after-the-fact justification.