Since early 1960s, we have a complete description of all possible [0,1]-based logical operations, namely of "and"-operations (t-norms) and of "or"-operations (t-conorms). In some real-life situations, intervals provide a more adequate way of describing uncertainty, so we need to describe interval-based logical operations. Usually, researchers followed a pragmatic path and simply derived these operations from the [0,1]-based ones. From the foundational viewpoint, it is desirable not to a priori restrict ourselves to such derivative operations but, instead, to get a description of all interval-based operations which satisfy reasonable properties.
Such description is presented in this paper. It turns out that all such operations can be described as the result of applying interval computations to the corresponding [0,1]-based ones.