Epistemic modal verbs and adverbs of necessity are claimed to be positive polarity items. We study their behavior by examining modal spread, a phenomenon that appears redundant or even anomalous, since it involves two apparent modal operators being interpreted as a single modality. We propose an analysis in which the modal adverb is an argument of the MUST modal, providing a meta-evaluation O which ranks the Ideal, stereotyp-ical worlds in the modal base as better possibilities than the Non-Ideal worlds in it. MUST and possibility modals differ in that the latter have an empty O, a default that can be negotiated. Languages vary in the malleability of this parameter. Positive polarity is derived as a conflict between the ranking imposed by O-which requires that the Ideal worlds be better possibilities than Non-Ideal worlds-and the effect of higher negation which renders the Ideal set non-homogenous. Applying the ordering over such a non-homogeneous set would express preference towards both p and ¬p worlds thus rendering the sentence uninformative. Negative polarity MUST and possibility modals, on the other hand, contain an empty O, application of higher negation therefore poses no problem. This account is the first to connect modal spread to positive polarity of necessity modals, and captures the properties of both in a unified analysis.