Solomon Asch’s conformity experiments used a simple visual judgment to expose a consequential social pressure: people may publicly agree with a group without privately believing it. The experiments showed both the reach of conformity and its fragility: one person who voiced the accurate answer could make it much easier for others to do the same.

Experimental Setup

Asch assembled groups of seven to nine people to judge which of three lines matched a line printed on a white card. Only one participant in each group was an unwitting subject; the others were confederates working with the experimenter. The subject sat at the end of the row, and everyone stated a choice aloud, making the group’s judgments public and sequential.

The experiment used twelve cards. On the first two, everyone identified the same matching lines. Beginning with the third, the confederates deliberately selected lines that were clearly not the same length as the reference line. The subject therefore had to answer after hearing a unanimous group announce a judgment that contradicted what was visible on the card.

Conformity Under Pressure

The unexpected unanimity unsettled participants. Some shifted their heads to view the lines from another angle, stood to inspect them more closely, or joked nervously about whether they were seeing things. These reactions registered the tension between visible evidence and the group’s confident public answer.

A significant number nevertheless went along with the group. Most subjects gave their own view most of the time, but 70 percent changed their real opinion at least once, and a third conformed at least half the time. In later conversations, most emphasized their wish to go along rather than stand out. Their conformity did not mean that they had come to believe the incorrect judgment; they were willing to say it to avoid separating themselves from the others.

The Effect of an Ally

Asch also tested what happened when the unanimous group was no longer unanimous. In one variation, a confederate gave the answer that matched the line on the card instead of joining the others’ incorrect responses. That one ally made a substantial difference: subjects who had someone on their side were more willing to state what they thought, and conformity fell sharply.

The contrast shows that group pressure does not require members to censor dissent directly. A person can yield simply because challenging an apparently united group feels harder than changing a public answer. Conversely, even one visible disagreement can weaken the impression that dissent is futile and give others room to speak independently.

Significance for Collective Judgment

The experiments distinguish conformity from groupthink while showing how both can undermine sound decisions. Groupthink reinforces shared assumptions by making disagreement seem improbable; conformity describes the individual’s willingness to voice agreement without privately accepting it. In Asch’s demonstration, the social setting altered what people said even though the lines supplied a direct basis for judgment.

The book uses this result to explain why diversity matters beyond supplying a group with different information: it can also protect independence of judgment. That independence is essential to collective decisions that draw on many people’s separate knowledge. The ally in Asch’s experiment is therefore more than a counterexample to the majority; the ally changes the conditions under which others can report what they see.