#structure building
In the most recent versions of Chomskyan theory, Merge plays a central (if not the central) role. It is the only structure building operation available in the language faculty. This differs from earlier versions where Move was considered to be a separate structure building operation but Move has since been reconceived as a different type of Merge.
The Minimalist Program has reduced the architecture of the language faculty to the bare essentials (referred to as the ‘(virtually) conceptually necessary’ components). This means that there is a lexicon, a structure building computational system and (at least) two ‘interfaces’ with other cognitive systems (one semantic, the other phonological, broadly speaking). Items are selected from the lexicon and copied into the Numeration if they are to be used to construct a sentence. The Numeration is like a holding bay.
Merge, the structure building operation, takes two items and forms a set, i.e. X and Y merge to form {X,Y} (the theory also involves labelling the set but I’ll ignore that bit). Now, when I said above ‘a different type of Merge’ I did not mean that the operation itself varies, rather the difference between the types of Merge lies in where X and Y come from. There are three possibilities.
1) X and Y both come directly from the Numeration.
2) Either X or Y but not both comes directly from the Numeration.
3) Neither X nor Y come directly from the Numeration.
Option (1) is the type of Merge that gets structure building started. Without (1) there would be no structure.
Option (2) is the type of Merge called External Merge (EM) because one of the merging items is from the Numeration, i.e. comes from somewhere external to the structure that has already been built. Option (2) allows the structure built by option (1) to be extended by merging further items to already existing structure.
Option (3) is the type of Merge called Internal Merge (IM) and this is the current conception of movement. When an item moves, it is going from one place in the structure to another so the items that are merging both come from somewhere internal to the structure that has already been built.
Note that this assumes there is only one monolithic Numeration. If we wanted to merge two existing structures, we would have to add to the options above or modify our assumptions about the nature of the Numeration.
