The limitations of randomised controlled trials are pretty obvious, but their advocates have managed to convince nearly everyone that there is no alternative. There is. In 1867, The Lancet published a series of papers by Professor Joseph Lister, setting out his work in treating cases of compound fracture by using carbolic acid sprays to eliminate infection and so avoid amputation. This is one of the greatest breakthroughs of modern medicine, and anaesthesia and antibiotics originated in the same approach of experiment and observation. This approach to research is in the spirit of John Locke, and has been advocated over three decades by Dr Terry Moore, of Clare College, Cambridge. The application of models derived from social studies, which have tried to apply the methods of the physical sciences in fields for which they were not designed, has tied us in a knot that has made it impossible to investigate anything without prohibitive cost. To take just one snag, medical trials are double blind by design, and we can't have a blind trial in education, as the teachers need to know what they are doing. The RCT model has then set tight limits on what can be investigated at any one time - it is virtually impossible, for example, to investigate one form of grammatical teaching against another, and against none at all. Lord Lister and Dr Moore provide the means to cut through the knot.