I argue that ‘conspiracy theory’ and ‘conspiracy theorist’ as commonly employed are ‘tonkish’ terms (as defined by Arthur Prior and Michael Dummett), licensing inferences from truths to falsehoods; indeed, that they are mega-tonkish terms, since their use is governed by different and competing sets of introduction and elimination rules, delivering different and inconsistent results. Thus ‘conspiracy theory’ and ‘conspiracy theorist’ do not have determinate extensions, which means that generalizations about conspiracy theories or conspiracy theorists do not have determinate truth-values. Hence (...) conspiracy theory theory – psychological or social scientific research into conspiracy theorists and what is wrong with them – is often about as intellectually respectable as an enquiry into bastards and what makes them so mean. (shrink)