1918-1959, worked at Uni. of California. His stay at Uni. of California was interrupted, when he was dismissed for refusing to sign a loyalty oath. He led a fight against the loyalty oath as an infringement (违反,侵害) on academic freedom and was
“If I had to reduce all educational psychology just one principle, I would say this: The most important single factor influencing learning is what the learner already knows. Ascertain this and teach him accordingly