Solomon Asch Asked People to Compare Three Lines and Watched Them Lie

Solomon Asch wanted to test how much social pressure could distort a perceptual judgment that, alone, almost no one got wrong. In 1951, he set the experiment up at Swarthmore. A subject sat with seven other students at a table. The experimenter held up a card with one vertical line and a second card with three lines of clearly different lengths. Each person, in turn, had to say which of the three matched the reference. The seven other students were Asch's confederates. The subject answered last.

For the first few trials the confederates gave the right answer. Then, on a pre-arranged signal, all seven gave the same wrong one. The line was visibly shorter or longer than the match they were endorsing. The subject sat with what they could see and what every other person at the table was saying.

Across 50 subjects and 18 trials each, Asch found that about 75 percent of subjects conformed to the wrong answer at least once, and the average rate of conformity was 36.8 percent of all critical trials. A control group, with no confederates, was wrong less than 1 percent of the time.

What made the result more interesting was the post-experiment interview. Some subjects insisted they had genuinely come to see the wrong line as the right one. Most, when pressed, admitted they had seen the truth and gone along anyway, fearing they were the strange one. A handful resisted every trial and reported feeling alarmed but cleansed.

Later work has shown the effect drops sharply if even a single confederate dissents. The 36 percent figure is not a fact about humans. It is a fact about humans facing a unanimous group.