 This was the beginning of one of the most epic controversies in the history of 20th Century biochemistry. It took the larger part of a decade to resolve this issue, time during which several laboratories claimed success in finding the elusive chemical intermediate. But none of these findings survived critical scrutiny. On the other side, all the evidence adduced by Mitchell and his few supporters was considered non-conclusive for the reasons mentioned above. Weber (2002) shows that the two competing theories of oxidative phosphorylation can be viewed as incommensurable in the sense of T.S. Kuhn (1970), without thereby being incomparable (as Kuhn is often misread).