What underpins acceptance of scientific theories by non-scientists? In a recent argument about climate change, I maintained that, as a non-specialist, I’m not in a position to judge the validity of theories or critiques of theories of anthropogenic climate change but I instead have to make a judgement about the reasonableness of believing in statements that a certain body of people make about the world. My point was that in the absence of any dramatic evidence to the contrary it’s much more reasonable to believe that the IPCC (and almost everyone else) is right than it is to believe either that there’s a huge con or a huge mistake. I think this is right but am I missing something more?