In this article, Rough Logic is defined as a nonstandard logic on a given information system IS = (U, A). Atomic formulae of the logic are defined as a = v or a
. It is interpreted as a(x) = v, where a ∈ A is an attribute in A, x is an individual variable on U, and v is an attribute value. The compound formula consist of the atomic formulae and logical connectives. Semantics of the logic
is ... [Show full abstract] discussed. Truth value of the rough logic is defined as a ratio of the number of elements satisfying the logical formula
to the total of elements on U. Deductive reasoning and resolution reasoning are also studied. The rough logic will offer a new idea for the applications
to classical logic and other nonstandard logic.