The important thing to note about interactional expertise is that the only thing the social researcher can’t do that a practicing plumber or physicist can do is the practical work of actually installing central heating or conducting experiments. It is this difference – the difference between being able to talk like a plumber/physicist and actually do plumbing/physics – that is the difference between interactional expertise (what the researcher has) and contributory expertise (what the plumbers and physicists have). Of course, plumbers and physicists who can talk fluently about their work will have both kinds of expertise.