 Epilogismos must be conducted with due diligence and caution (e.g., §3, xxix 1–4), but this seems an inadequate defense against the possibility raised by their opponents that counter-examples to generalizations—unique individuals or rare species—may always exist undiscovered. More convincing is the response that, since freaks and rarities were discovered empirically, to project the existence of such things into unknown realms is simply to apply the SM (e.g., §3, xxviii 29–37). While this does not prove that the EM is superfluous, it does raise another unsettled question, whether all these Epicureans believe that there is only one mode of sign-inference, the SM, or two (as suggested by Zeno in §1, e.g., xii 2–31). It is probably helpful to see this problem in light of a basic disagreement that emerges in On Signs between the Epicureans and their opponents: that the Epicureans are mainly concerned, not with arriving, somehow or other, at true beliefs, but with how we can be certain that our beliefs are true, experience being the only secure foundation for any property-projection. Sign-inferences here and in other sources often take the form of a conditional (sunêmmenon), such as: ‘If there is smoke, there is fire’, or a para-conditional (parasunêmmenon), such as ‘Since there is smoke, there is fire’ (equivalent to a conditional plus its antecedent), and the EM is built around a criterion of truth for conditionals: the antecedent must be ‘eliminated’, or negated, simply by the ‘elimination’ of the consequent (§1, xii 1–14). In the void/movement case, then, if movement is a sign of void, elimination of void thereby eliminates movement, and the inference seems to be valid by the EM.