Merge is one of the basic operations in the Minimalist Program, a leading approach to generative syntax, when two syntactic objects are combined to form a new syntactic unit. Merge also has the property of recursion in that it may apply to its own output: the objects combined by Merge are either lexical items or sets that were themselves formed by Merge. This recursive property of Merge has been claimed to be a fundamental characteristic that distinguishes language from other cognitive faculties. As Noam Chomsky puts it, Merge is "an indispensable operation of a recursive system... which takes two syntactic objects A and B and forms the new object G=".
Mechanisms of Merge
Within the Minimalist Program, syntax is derivational, and Merge is the structure-building operation. Merge is assumed to have certain formal properties constraining syntactic structure, and is implemented with specific mechanisms. In terms of a merge-base theory of language acquisition, complements and specifiers are simply notations for first-merge, and later second-merge establishes substantive 'base structure' inherent to the VP, yielding theta/argument structure, and may go beyond the lexical-category VP to involve the functional-category light verb vP. Internal-merge establishes more formal aspects related to edge-properties of scope and discourse-related material pegged to CP. In a Phase-based theory, this twin vP/CP distinction follows the "duality of semantics" discussed within the Minimalist Program, and is further developed into a dual distinction regarding a probe-goal relation. As a consequence, at the "external/first-merge-only" stage, young children would show an inability to interpret readings from a given ordered pair, since they would only have access to the mental parsing of a non-recursive set.. In addition to word-order violations, other more ubiquitous results of a first-merge stage would show that children's initial utterances lack the recursive properties of inflectional morphology, yielding a strict Non-inflectional stage-1, consistent with an incremental Structure building model of child language.
Merge takes two objects α and β and combines them, creating a binary structure.
Feature checking
In some variants of the Minimalist Program Merge is triggered by feature checking, e.g. the verb eat selects the noun cheesecake because the verb has an uninterpretable N-feature , which must be checked due to full interpretation. By saying that this verb has a nominal uninterpretable feature, we rule out such ungrammatical constructions as *eat beautiful. Schematically it can be illustrated as:
Projection and labeling
Recursion
External and internal Merge
Chomsky distinguishes between external and internal Merge: if A and B are separate objects then we deal with external Merge; if either of them is part of the other it is internal Merge.
Three controversial aspects of Merge
Standard Merge sentence structure is generated bottom upin the mind of speakers all syntactic structure is binary branching syntactic structure is constituency-based. While these three assumptions are taken for granted for the most part by those working within the broad scope of the Minimalist Program, other theories of syntax reject one or more of them. Merge is commonly seen as merging smaller constituents to greater constituents until the greatest constituent, the sentence, is reached. This bottom-up view of structure generation is rejected by representational theories, and it is contrary to early work inTransformational Grammar. The phrase structure rules of context free grammar, for instance, were generating sentence structure top down. Merge is usually assumed to merge just two constituents at a time, a limitation that results in tree structures in which all branching is binary. While the strictly binary branching structures have been argued for in detail, one can also point to a number of empirical considerations that cast doubt on these strictly binary branching structures, e.g. the results of standard constituency tests. For this reason, most grammar theories outside of Government and Binding Theory and the Minimalist Program allow for n-ary branching. Merge merges two constituents in such a manner that these constituents become sister constituents and are daughters of the newly created mother constituent. This understanding of how structure is generated is constituency-based. Dependency grammars disagree with this aspect of Merge, since they take syntactic structure to be dependency-based.
represents immediate constituency relations as well as linear precedence relations. In a PSG, a constituent contains at least one member, but has no upper bound. In contrast, with Merge theory, a constituent contains at most two members. Specifically, in Merge theory, each syntactic object is a constituent.
X-bar theory
is a template that claims that all lexical items project three levels of structure: X, X', and XP. Consequently, there is a three-way distinction between Head, Complement, and Specifier:
the Head projects its category to each node in the projection;
the Complement is introduced as sister to the Head, and forms an intermediate projection, labeled X';
While the first application of Merge is equivalent to the Head-Complement relation, the second application of Merge is equivalent to the Specifier-Head relation. However, the two theories differ in the claims they make about the nature of the Specifier-Head-Complement structure. In X-bar theory, S-H-C is a primitive, an example of this is Kayne's antisymmetry theory. In a Merge theory, S-H-C is derivative.
