Chapter 6 draws the conclusions of the historical review conducted in the previous chapters and critically reconsiders the notion of parameter, reevaluating both its role in Generative Grammar and its theoretical status. First, concerning Linearization parameters like the ones responsible for overt vs. covert wh-movement and head directionality, it is argued that linguistic variation can be attributed to PF-interface conditions having a disambiguating effect on a specific set of syntactic representations which cannot meet bare output conditions. Second, considering Roberts’s (2019) reformulation of argument-drop, verb movement, and V2 as instances of head movement, it is argued that Chomsky’s (2021a) extra-syntactic account of head movement suggests the possibility of developing a unified theory overcoming the duality between the ‘syntactic parameters’ accounting for the emergence of null arguments and verb movement on one side and Linearization parameters on the other. Lastly, the possibility that variation can arise in the narrow syntax is also considered, followed by some final remarks on the latest views on parametric variation in connection with current minimalist assumptions.

Chapter 3 focuses on the debate about the concept of parameter which took place during the first decade of the twenty-first century. The first two positions discussed are Kayne’s (2000, 2005) microparametric approach and Baker’s (2001, 2008) macroparametric approach. These two approaches are then confronted with Newmeyer’s (2004, 2005) criticism. Finally, two lines of linguistic inquiry which are particularly relevant to the evaluation of the notion of parameter are presented, namely Roberts and Holmberg’s (2010) hierarchical parametric model and Longobardi’s and his collaborators’ Parametric Comparison Method (PCM). On the one hand, Roberts and Holmberg’s (2010) model overcomes the limitations of micro- and macroparameters by combining a lexically based, microparametric view of linguistic variation with the idea that parametric variation is an emergent property of the interaction of Universal Grammar, primary linguistic data, and third factor considerations. On the other hand, the unprecedented results achieved by the PCM in establishing the genealogical relations among languages on the basis of syntactic comparison arguably attest to the validity of the parametric model.

Chapter 1 provides some background on the shift in emphasis from Universal Grammar (UG) to third factors and gives a description of selected third factors, e.g. the Inclusiveness Condition and the Extension Condition. The main emphasis is on the Labeling Algorithm and the Principle of Determinacy. Generative models focus on the faculty of language as represented in the mind/brain. UG is the “system of principles, conditions, and rules” that all languages share through biological necessity. However, although UG received a lot of attention, recently principles “grounded in physical law” and the general “capacity to acquire knowledge” have been emphasized more. This chapter also introduces two main reasons of language change that are responsible for the linguistic cycle: those caused by economy and those by innovation.