Phase-based Minimalist Parsing and complexity in non-local dependencies Cristiano Chesi NETS - IUSS P.zza Vittoria 15 I-27100 Pavia (Italy) [email protected] 1 Introduction Abstract The last twenty years of formal linguistic research English. A cognitively plausible parsing have been deeply influenced by Chomsky’s mini- algorithm should perform like the human malist intuitions (Chomsky 1995, 2013). In a nut- parser in critical contexts. Here I propose shell, the core Minimalist proposal is to reduce an adaptation of Earley’s parsing algo- phrase structure formation to the recursive appli- rithm, suitable for Phase-based Minimal- cation of a binary, bottom-up, structure-building ist Grammars (PMG, Chesi 2012), that is operation dubbed Merge. Merge creates hierar- able to predict complexity effects in per- chical structures by combining two lexical items formance. Focusing on self-paced reading (1.a), one lexical item and an already built (by pre- experiments of object clefts sentences vious application of Merge operations) phrase (Warren & Gibson 2005) I will associate (1.b) or two already built phrases (1.c). to parsing a complexity metric based on cued features to be retrieved at the verb (1) a. b. c. segment (Feature Retrieval & Encoding Cost, FREC). FREC is crucially based on x y x YP XP YP the usage of memory predicted by the dis- cussed parsing algorithm and it correctly Phrases are not linearly ordered by Merge. Only fits with the reading time revealed. when they are spelled-out (i.e. sent to the Sensory- Motor interface, aka Phonetic Form, PF), lineari- Italian. Un algoritmo di parsing cogniti- zation is required: assuming that x and y are ter- vamente plausibile dovrebbe avere una minal nodes (i.e. words), either <x, y> or <y, x> performance paragonabile a quella can both be proper linearizations of (1.a). Hierar- umana in contesti critici. In questo lavoro chical structure (and linearization) is also deter- propongo un adattamento dell’algoritmo mined by another structure building operation: di Earley che utilizza Grammatiche Mini- Move (or Internal Merge, Chomsky 1995); Move maliste basate sul concetto di Fase (PMG, re-arranges phrases in the structure by re-merging Chesi 2012). Associata all’algoritmo, an item (already merged in the structure) to the verrà discussa una funzione di costo (Fea- edge of the current, top-most, phrase: for instance ture Retrieval & Encoding Cost, FREC) [XP [YP [ZP]]] can lead to [ZP [XP [YP (ZP)]] if capace di misurare la difficoltà relativa al XP (the probe) has a feature triggering movement recupero dei referenti coinvolti in dipen- (e.g. +f) and ZP (the goal) has the relevant feature denze a distanza. La funzione si basa sui qualifying it as a plausible target for movement tratti morfosintattici archiviati nel me- (e.g. -f). At the end, the element displaced (ZP) mory buffer utilizzato dal parser. Concen- will occupy the edge of the structure. When the trandosi sulle strutture scisse ad estra- items within an already built phrase, for instance zione dell’oggetto, si mostrerà come il XP, are delivered to PF, they get properly linear- FREC risulti predittivo dei dati sperimen- ized according to their hierarchical structure (e.g. tali ricavati da studi classici di lettura au- Linear Correspondence Axiom, Kayne 1994), in- toregolata (Warren & Gibson 2005). trinsic phonetic properties (e.g. cliticization), as well as economy conditions (e.g. an items should with wh-questions share a similar non-local de- not be pronounced twice). Such a (cyclic) spell- pendency formation: out happens at phases: XP will be delivered to PF only if it qualifies as a phase (Chomsky 2013). In (2) a. It is [DP1 the banker|John|me] that this sense, a phase should be a constituent/phrase [DP2 the lawyer|Dan|you] will meet _DP1 with some degree of completeness with respect to semantic interpretation (Logic Form, aka LF). In short, the head of the dependency (DP1) should Most minimalist linguists agree on the fact that a be interpreted both as a focalized item and as the full-fledged sentence (aka Complementizer direct object (this is where the name of the con- Phrase, CP) is a phase, the highest argumental struction “object cleft” comes from) of the embed- shell of a predicate qualifies as a phase (aka little- ded verb. The difficulty of parsing this structure v Phrase, vP) and also a full argument is a phase has been deeply discussed in literature (Gordon et (aka Determiner Phrase, DP). Such a simple (and al. 2004). What is considered a crucial factor is the computationally appealing) model has been fully role of the similarity between DP1 and DP2 (the formalized (Stabler 1997, Collins & Stabler 2016) subject of the cleft, Belletti and Rizzi 2013, §2). and some parsing algorithm that implements main To capture this fact, I will re-adapt Earley’s algo- minimalist insights has been discussed in litera- rithm (§3.1) to operate on a specific version of ture (e.g. Harkema 2001, Chesi 2012 a.o.). Minimalist Grammar (§3). This would allow us to In these pages, I will present some of the ad- subsume the similarity effect by predicting read- vantages of retaining such a simplified computa- ing differences as revealed in self-paced reading tional approach to syntactic derivation. Crucially, experiments (e.g. Warren & Gibson 2005, §4). I will try to overcome some clear disadvantages in assuming the just presented standard, bottom-up, 2 Parsing with Minimalist Grammars structure building operations, while obtaining, at Since Merge and Move strictly operate “from bot- the same time, a better empirical fit: on the one tom to top”, we expect sentence structure in (2) to hand, I will avoid any non-efficient deductive- be built in 9 steps (and 5 phases: ph1, ph2 …): parsing perspective (that is a consequence of the assumed bottom-up nature of the Merge and 1. [ph1 the banker] Move operations); on the other, I will promote a 2. [ph3 meet [ph1 …]]] more transparent relation between formal compe- 3. [ph3 will [meet [ph1 …]]] tence, parsing and psycholinguistic performance 4. [ph2 the lawyer] (independently built) by presenting a simple adaptation of Earley’s 5. [ph3 [ph2 …] will [meet [ph1 …]]] 6. [ph4 that [ph3 [ph2 …] will [meet [ph1 …]]]] Top-Down parsing algorithm (Earley 1970) and a 7. [[ph1 …] [ph4 that [ph3 [ph2 …] will [meet (ph1 …)]]]] complexity metric that refers directly to parsing (ph1 moves to ph4 edge) memory usage: this metric will be able to account 8. [ph5 is [[ph1 …] [ph4 that [ph3 [ph2 …] will [meet for complexity in retrieving the correct item while [ph1 …]]]]] 9. [ph5 it [is [[ph1 …] [ph4 that [ph3 [ph2 …] will [meet processing specific non-local dependencies. By [ph1 …]]]]] “non-local” dependencies I refer to those relations involving movement, namely constructions where With the exception of step 4, all other steps must the very same item occurs in two distinct, non-ad- be strictly ordered. As a consequence, moving the jacent, positions: for instance, wh-dependencies in direct object in the relevant position would force English require the wh- item (who, in (1)) to be the linearization to place ph2 first at the edge of interpreted both in a the left peripheral (focalized) ph3, then at the edge of ph4. This is how Minimal- position (the Criterial position, in the sense of ism derives the relevant non-local dependencies in Rizzi 2007) and in the thematic lower position (2). Obviously this is not transparent at all with 1 (right next to the verb meet in (1)) : respect to parsing (e.g. Fong 2011), where the pro- cessing order is expected to be completely re- (1) Who1 do you think Mary will meet _1? versed: The critical derivation I will discuss in this pa- 1. [ph5 ] is initiated per is that of object clefts (Gordon et al. 2001) that 2. [ph1 ] is fully processed while [ph5 ] is still open 1 Coreference in non-local dependencies will be indi- pronounced item in the thematic position is indicated cated by the same subscript placed both on the “dis- with a co-indexed underscore) placed” item and on the thematic position (the non- 3. [ph4 ] is initiated (a Relative Clause) As in MGs (Stabler 1997), the Lexicon is a finite 4. [ph3 ] is initiated as well (Verbal Phrase) set of lexical items storing phonetic, semantic 5. [ph2 …] is fully processed while [ph5 ], [ph4 ] and [ph3 ] are open (here ignored) and syntactic features (functional 6. [ph1 ] finally receives a thematic role, hence [ph5 ], [ph4 ] +F, selectional =S, categorial C); an item bearing and [ph3 ] can be closed. a selection feature, e.g. [=XP A], requires an XP ph(r)ase right afterward: [=XP A [XP ]] (once fea- Unless we deeply revise Minimalist Grammars tures are projected in the structure, i.e. [XP ], the (both with respect to movement, Fong 2005, and selection features are deleted, i.e. =XP); functional to thematic role assignment, Niyogi & Berwick features, e.g. +X express a functional specifica- 2005), we are left with an asymmetry that can not tion like determiner +D, tense +T or topic +S be explained simply in terms of structure building (when placed under brackets, e.g. (+f), functional operations as discussed in the next section. features are optional; Ø indicates phonetically null items). 2.1 The “similarity” problem Merge simply unifies the expected structure built Warren & Gibson (2005) show that in clefts con- so far with a new incoming item, if and only if, structions like the one discussed in (2), the varia- this item bears (at least) the first relevant feature tion of the two DPs [ph1 ] and [ph2 ] produces dif- expected (Merge operation is greedy: an item ferences in reading time at the verb segment in bearing more features in the correct expected or- self-paced reading experiments with the full-DP der will lexicalize them all): matching condition ([ph1 the barber] that [ph2 the banker] praised …) and proper nouns matching 1.