Away from their profession, scientists are inherently no more honest or ethical than other people. But in their profession they work in an arena that puts a high premium on honesty. The cardinal rule in science is that all claims must be testable --- they must be capable,at least in principle, of being proved wrong. For example, if someone claims that a certainprocedure has a certain result, it must in principle be possible to perform a procedure that will either confirm or contradict the claim. If confirmed, then the claim is regarded as useful and a stepping-stone to further knowledge. None of us has the time or energy or resources to test every claim, so most of the time we must take somebody's word. However, we must have some criterion for deciding whether one person's word is as good as another's andwhether one claim is as good as another. The criterion, again, is that the claim must be testable. To reduce the likelihood of error, scientists accept the word only of those whose ideas, theories, and findings are testable -- if not in practice then at least in principle.Speculations that cannot be tested are regarded as "unscientific." This has the long-run effect of compelling honesty --- findings widely publicized among fellow scientists are generallysubjected to further testing. Sooner or later, mistake (and lies) are bound to be found out; wishful thinking is bound to be exposed. The honesty so important to the progress of science thus becomes a matter of self-interest to scientists.