The mental space is a theoretical construct proposed by Gilles Fauconnier[1] 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.
[2] Building of mental spaces and establishment of mappings between those mental spaces are the two main processes involved in construction of meaning.
[4] Space builders can be expressions like prepositional phrases, adverbs, connectives, and subject-verb combinations that are followed by an embedded sentence.
They require hearers to establish scenarios beyond the present point of time.