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In formal logic, a moal logic is any system of formal logic that attempts to deal with modalities. Traditionally, there are three 'modes' or 'moods' or 'modalities' of the copula to be, namely, possibility, probability, and necessity. Logics for dealing with a number of related terms, such as eventually, formerly, can, could, might, may, must, are by extension also called modal logics, since it turns out that these can be treated in similar ways.