Modus tollens argument

FIGURE 4.1 The application of the modus tollens form of argument to a three-taxon statement. H1.3 = Hypotheses 1-3. For further explanation see text. (After Cartmill, M., Z Zoo/. Syst EvoL, 19, 73-96, 1981.)... 

Lakatos needs a critical evaluation of theories in his system just as much as Popper, and just like Popper he did not allow ad hoc auxiliary hypotheses that are not independently testable to distort such critical evaluation of competing theories. Both Lakatos and Popper understood hypotheses in the sense of universal propositions and both employed the modus tollens form of argument. Whether the emphasis is on corroboration or falsification, this very distinction cannot be had outside Popper s solution to the logical problem of induction, for it only can provide that very asymmetry, and hence the basis on which to distinguish falsificationism from verificationism. ... 

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