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 (a set). Merge also has the property of recursion in that it may be applied 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 (1999) 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=" (p. 2).[1]
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 (read as "complement-of" [head-complement]), and later second-merge (read as "specifier-of" [specifier-head]), with merge always forming to a head. First-merge establishes only a set and is not an ordered pair. In its original formulation by Chomsky in 1995 Merge was defined as inherently asymmetric; in Moro 2000 it was first proposed that Merge can generate symmetrical structures provided that they are rescued by movement and asymmetry is restored [2] For example, an -compound of 'boat-house' would allow the ambiguous readings of either 'a kind of house' and/or 'a kind of boat'. It is only with second-merge that order is derived out of a set which yields the recursive properties of syntax. For example, a 'House-boat' now reads unambiguously only as a 'kind of boat'. It is this property of recursion that allows for projection and labeling of a phrase to take place;[3] in this case, that the Noun 'boat' is the head of the compound, and 'house' acting as a kind of specifier/modifier. External-merge (first-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 (second-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.[4] 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. (See Roeper for a full discussion of recursion in child language acquisition).[5] 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.[6]
Merge takes two objects α and β and combines them, creating a binary structure.
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 [uN] ("u" stands for "uninterpretable"), which must be checked (or deleted) due to full interpretation.[7] By saying that this verb has a nominal uninterpretable feature, we rule out such ungrammatical constructions as *eat beautiful (the verb selects an adjective). Schematically it can be illustrated as:
There are three different accounts of how strong features force movement:[8] [9]
1. Phonetic Form (PF) crash theory (Chomsky 1993) is conceptually motivated. The argument goes as follows: under the assumption that Logical Form (LF) is invariant, it must be the case that any parametric differences between languages reduce to morphological properties that are reflected at PF (Chomsky 1993:192). Two possible implementations of the PF crash theory are discussed by Chomsky:
PF crash theory: A strong feature that is not checked in overt syntax causes a derivation to crash at PF.2. Logical Form (LF) crash theory (Chomsky 1994) is empirically motivated by VP ellipsis. LF crash theory: A strong feature that is not checked (and eliminated) in overt syntax causes a derivation to crash at LF.3. Immediate elimination theory ((Chomsky 1995)) Virus theory: A strong feature must be eliminated (almost) immediately upon its introduction into the phrase marker; otherwise, the derivation cancels.
Initially, the cooperation of Last Resort (LR) and the Uniformity Condition (UC) were the indicators of the structures provided by Bare Phrase which contain labels and are constructed by move, as well the impact of the Structure Preservation Hypothesis.[10]
When we consider the features of the word that provide the label when the word projects, we assume that the categorical feature of the word is always among the features that become the label of the newly created syntactic object.[12] In this example below, Cecchetto demonstrated how projection selects a head as the label.
In this example by Cecchetto (2015), the verb "read" unambiguously labels the structure because "read" is a word, which means it is a probe by definition, in which "read" selects "the book".the bigger constituent generated by merging the word with the syntactic objects receives the label of the word itself, which allow us to label the tree as demonstrated.
In this tree, the verb "read" is the head selecting the DP "the book", which makes the constituent a VP.
Merge operates blindly, projecting labels in all possible combinations. The subcategorization features of the head act as a filter by admitting only labelled projections that are consistent with the selectional properties of the head. All other alternatives are eliminated. Merge does nothing more than combine two syntactic objects (SO’s) into a unit, but does not affect the properties of the combining elements in any way. This is called the No Tampering Condition (NTC). Therefore, if α (as a syntactic object) has some property before combining with β (which is likewise a syntactic object) it will still have this property after it has combined with β. This allows Merge to account for further merging, which enables structures with movement dependencies (such as wh-movement) to occur. All grammatical dependencies are established under Merge: this means that if α and β are grammatically linked, α and β must have merged.[13]
A major development of the Minimalist Program is Bare Phrase Structure (BPS), a theory of phrase structure (structure building operations) developed by Noam Chomsky in 1994.[14] BPS is a representation of the structure of phrases in which syntactic units are not explicitly assigned to categories.[15] The introduction of BPS moves the generative grammar towards dependency grammar (discussed below), which operates with significantly less structure than most phrase structure grammars.[16] The constitutional operation of BPS is Merge. Bare phrase structure attempts to: (i) eliminate unnecessary elements; (ii) generate simpler trees; (ii) account for variation across languages.[17]
Bare Phrase Structure defines projection levels according to the following features:[10]
The minimalist program brings into focus four fundamental properties that govern the structure of human language:[18] [19]
Context-sensitive phrase-structure (PS) rules ABC → ADC B = single symbol A, C, D = string of symbols (D = non-null, A and C can be null) A and C are non-null when the environment in which B needs to be re-written as D is specified.
Context-free phrase-structure (PS) rules B → D B = single non-terminal symbol D = string of non-terminal symbols (can be non-null) where lexical items can be inserted with their subcategorization features
Since the publication of bare phrase structure in 1994., other linguists have continued to build on this theory. In 2002, Chris Collins continued research on Chomsky's proposal to eliminate labels, backing up Chomsky's suggestion of a more simple theory of phrase structure.[20] Collins proposed that economy features, such as Minimality, govern derivations and lead to simpler representations.
In more recent work by John Lowe and John Lundstrand, published in 2020, minimal phrase structure is formulated as an extension to bare phrase structure and X-bar theory. However it does not take adopt all of the assumptions associated with the Minimalist Program (see above). Lowe and Lundstrand argue that any successful phrase structure theory, should include the following seven features:
Although Bare Phrase Structure includes many of these features, it does not include all of them, therefore other theories have attempted to incorporate all of these features in order to present a successful phrase structure theory.
Chomsky (2001) 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.[21]
As it is commonly understood, standard Merge adopts three key assumptions about the nature of syntactic structure and the faculty of language:
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 (non-derivational) theories (e.g. Generalized Phrase Structure Grammar, Head-Driven Phrase Structure Grammar, Lexical Functional Grammar, most dependency grammars, etc.), and it is contrary to early work in Transformational Grammar. The phrase structure rules of context free grammar, for instance, were generating sentence structure top down.
The Minimalist view that Merge is strictly binary is justified with the argument that an
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n\geq3
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n\geq3
k(n-1)+1
k\geq1
k(n-1)+1
n
n\geq3
Further,
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n\geq3
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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 (as opposed to dependency-based). Dependency grammars (e.g. Meaning-Text Theory, Functional Generative Description, Word grammar) disagree with this aspect of Merge, since they take syntactic structure to be dependency-based.[24]
In other approaches to generative syntax, such as Head-driven phrase structure grammar, Lexical functional grammar and other types of unification grammar, the analogue to Merge is the unification operation of graph theory. In these theories, operations over attribute-value matrices (feature structures) are used to account for many of the same facts. Though Merge is usually assumed to be unique to language, the linguists Jonah Katz and David Pesetsky have argued that the harmonic structure of tonal music is also a result of the operation Merge.[25]
This notion of 'merge' may in fact be related to Fauconnier's 'blending' notion in cognitive linguistics.
Phrase structure grammar (PSG) represents immediate constituency relations (i.e. how words group together) as well as linear precedence relations (i.e. how words are ordered). 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:
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 (S-H-C) 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.