Uploaded August 2014 | Updated September 2026, 2 weeks ago

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Imagine you are a university student. You are waiting for the first session of ‘Introductory Economics 70’ to begin. Then somebody comes in and says that something has happened to the professor who normally teaches the course, so a stand-in instructor will deliver the lecture. The only thing is that, because the department would like some feedback, the students will be asked to fill in an evaluation form afterwards. By way of introduction, each student is given a slip of paper with some information about this lecturer. Naturally (as this was in fact a Psychology experiment – although students did not know it) there were two versions of this short bio. Here they are. Can you spot the difference?
A: “Mr Long is a graduate student in the Department of Economics and Social Science here at MIT. He has had three semesters of teaching experience in psychology at another college. This is his first semester teaching Ec 70. He is 26 years old, a veteran, and married. People who know him consider him to be a very warm person, industrious, critical, practical and determined”.
B: “Mr Long is a graduate student in the Department of Economics and Social Science here at MIT. He has had three semesters of teaching experience in psychology at another college. This is his first semester teaching Ec 70. He is 26 years old, a veteran, and married. People who know him consider him to be a rather cold person, industrious, critical, practical and determined”.
That’s right. The only difference is two words: ‘very warm’ as opposed to ‘rather cold’. Would that tiny detail make a difference? Watch the great Paul Bloom describe the study and explain why expectations matter so much…


[NB: I do not own the copyright to this video clip. I have uploaded it here for educational purposes].