Why does a three year-old say “I went,” then six months later starts saying “I goed”? When you first heard the word “fax,” how did you know the past tense is “faxed”? And why is it that a baseball player is said to have “flied out,” but could never have “flown out”?

After fifteen years of studying words in history, in the laboratory, and in everyday speech, Steven Pinker has worked out the dynamic relationship – searching memory vs. following rules – that determines the forms our speech takes. In one of his final lectures at MIT Pinker gives the ultimate lecture on verbs, in a rich mixture of linguistics, cognitive neuroscience, and humor.

http://mitworld.mit.edu/video/143