The optimal situation would be that UG reduces to the simplest computational principles which operate in accord with conditions of computational efficiency. This conjecture is ... called the Strong Minimalist Thesis (SMT).
Under the Strong Minimalist Thesis, language is a product of the interface requirements and social exposure to particular languages (amongst other things). This reduces to a minimum the "innate" component of the language faculty, which has been criticized over many decades.
Intrinsic to the syntactic model (e.g. the Y/T-model) is the fact that social and other factors play no role in the computation that takes place in narrow syntax; what Chomsky, Hauser and Fitch refer to as Faculty of Language in the Narrow Sense (FLN), as distinct from Faculty of Language in the Broad Sense (FLB). Thus, Narrow Syntax only concerns itself with interface requirements, also called legibility conditions. SMT can be restated as follows: syntax, narrowly defined, is a product of the requirements of the interfaces and nothing else. This is what is meant by "Language is an optimal solution to legibility conditions". (Chomsky 2001:96)
Interface requirements force deletion of features that are uninterpretable at a particular interface, a necessary consequence of Full Interpretation. A PF object must only consist of features that are interpretable at the articulatory-perceptual (A-P) interface; likewise a LF object must consist of features that are interpretable at the conceptual-intentional (C-I) interface. The presence of an uninterpretable feature at either interface will cause the derivation to crash.
Narrow syntax proceeds as a set of operations — Merge, Move and Agree — carried out upon a numeration (a selection of features, words etc., from the lexicon) with the sole aim of removing all uninterpretable features before being sent via Spell-Out to the A-P and C-I interfaces. The result of these operations is a hierarchical syntactic structure that captures the relationships between the component features.
More recent versions of minimalism recognize three operations: Merge (i.e. external Merge), Move (i.e. internal Merge), and Agree. The emergence of Agree as a basic operation is related to the mechanism which forces movement, which is mediated by feature-checking.
In its original formulation, Merge is a function that takes two objects (α and β) and merges them into an unordered set with a label, either α or β. In more recent treatments, the possibility of the derived syntactic object being un-labelled is also considered; this is called "simple Merge" (see Label section).
In each of these cases, there is no lexical item acting as a prominent element (i.e. a head). Given this, it is not possible through minimal search to extract a label for the phrase. While Chomsky has proposed solutions for these cases, it has been argued that the fact that such cases are problematic suggests that the labeling algorithm violates the tenets of the minimalist program, as it departs from conceptual necessity.
Other linguistic phenomena that create instances where Chomsky's labeling algorithm cannot assign labels include predicate fronting, embedded topicalization, scrambling (free movement of constituents), stacked structures (which involve multiple specifiers).
Starting in the early 2000s, attention turned from feature-checking as a condition on movement to feature-checking as a condition on agreement. This line of inquiry was initiated in Chomsky (2000), and formulated as follows:
The spell-out of a string is assumed to be cyclic, but there is no consensus about how to implement this. Some analyses adopt an iterative spell-out algorithm, with spell-out applying after each application of Merge. Other analyses adopt an opportunistic algorithm, where spell-out applies only if it must. And yet others adopt a wait-til-the-end algorithm, with spell-out occurring only at the end of the derivation.
There is no consensus about the cyclicality of the Agree relation: it is sometimes treated as cyclic, sometimes as a-cyclic, and sometimes as counter-cyclic.
The main reasoning behind the transition from X-bar theory to BPS is the following:
Much research has been devoted to the study of the consequences that arise when minimalist questions are formulated. The lists below, which are not exhaustive, are given in reverse chronological order.