Noted ethics philosopher and Nobel Laureate Bertrand Russell once was questioned by the Harvard Board of Governors about having an extramarital affair with a student. When faced with the hypocrisy of being an ethics professor engaged in immoral conduct, Russell argued his private affairs had nothing to do with his professional duties. “But you are a Professor of Ethics!” maintained one of the board members. “I was [also] a Professor of Geometry at Cambridge,” Russell rejoined, but “they never asked me why I was not a triangle.” Lecturing on ethics was a job for Russell; it didn’t mean he had to live an ethical life.
Should we listen to someone who chose to teach ethics by day and betray it by night? Should we expect a speaker to vouch for his opinion through his own conduct? The law teaches us to ascribe less weight to an opinion when the speaker suffers from a credibility problem. But what constitutes a credible source? Lawyers who engage in the presentation of evidence devote a lot of mental energy to this question. Whether the trier of fact believes a witness’s testimony about a disputed fact — or, more particularly here, his opinion on a subject on which he is proffered as an expert — is everything to a case.
