The mental space is a theoretical construct proposed by Gilles Fauconnier corresponding to possible worlds in truth-conditional semantics. The main difference between a mental space and a possible world is that a mental space does not contain a faithful representation of reality, but an idealized cognitive model. Building of mental spaces and establishment of mappings between those mental spaces are the two main processes involved in construction of meaning.
It is one of the basic components in Gilles Fauconnier and Mark Turner's blending theory, a theory within cognitive semantics.
Base space and built space
Base space, also known as reality space, presents the interlocutors' shared knowledge of the real world. Space builders are elements within a sentence that establish spaces distinct from, yet related to the base space constructed.