The sorites as a formal theory. The sorites paradox has been understood as a failure of classical logic and a way out can be found by choosing a non classical logic (fuzzy logic, for instance). We understand the sorites not as a problem of logic but of ontology, so we preserve classical logic and submit the premisses of the argument to a deeper analysis. As a result we obtain two theories for soritical arguments and enlighten the kind of structure requested by these arguments. The former theory has a lattice theoretic flavor and is fitted for paradoxes like “the heap” and “the bald man”; the latter is group theoretic in character and can manage paradoxes based on observational predicates like “tall”, “red” and so on. In both cases the contradiction is derived from a larger set of hypotheses than in usual analysis and some of these hypotheses make assertions whose empirical meaning can be questioned.