1 In a number of recent presentations most notably at FME 96 oneofthe foremost scientists in the ?eld of formal methods, C.A.R. Hoare, has highlighted the fact that formal methods are not the only technique for producing reliable software. This seems to have caused some controversy, not least amongst formal methods practitioners. How can one of the founding fathers of formal methods seemingly denounce the ?eld of research after over a quarter of a century of support? This is a question that has been posed recently by some formal methods skeptics. However, Prof. Hoare has not abandoned formal...