The paper makes three points about the role of double dissociation in cognitive neuropsychology. First, arguments from double dissociation to separate modules work by inference to the best, not the only possible, explanation. Second, in the development of computational cognitive neuropsychology, the contribution of connectionist cognitive science has been to broaden the range of potential explanations of double dissociation. As a result, the competition between explanations, and the characteristic features of the assessment of theories against the criteria of probability and explanatory value, are more visible. Third, cognitive neuropsychology is a division of cognitive psychology but the practice of cognitive neuropsychology proceeds on assumptions that go beyond the subject matter of cognitive psychology. Given such assumptions, neuroscientific findings about lesion location may enhance the value of double dissociation in shifting the balance of support between cognitive theories.