This dissertation argues for an Optimality Theoretic analysis of 
 

null subjecthood, subject inversion, agreement and structural case 
 

assignment. It does so on the basis of the hypothesis that an analysis 
 

in terms of the interaction of violable, conflicting constraints adds 
 

to the deductive structure of linguistic explanations while simplifying 
 

the definition of the relevant syntactic modules. 
 

	Among the most relevant results is a unified analysis of the 
 

crosslinguistic and language-internal distribution of null and 
 

inverted subjects. An initial investigation shows that subjects are 
 

null when referring to antecedents with topic status, and inverted 
 

when focused, a result formalized through the constraints DropTopic 
 

and AlignFocus. The interaction between these constraints and the 
 

constraints Subject and Parse, favoring subjects in preverbal subject 
 

position, determines the distribution of null subjects language-
 

internally and crosslinguistically, eliminating the need for an 
 

independent pro-drop parameter (Grimshaw & Samek-Lodovici 1995).
 

	A second result concerns expletives, whose language specific 
 

inventories are shown to follow to a high degree from the interaction 
 

between the above constraints and Full-Int, a constraint requiring 
 

that all constituents be interpreted. This shows that expletive 
 

inventories can be derived by way of grammar, with no recourse to 
 

lexical stipulation (PrinceÊ&ÊSmolensky 1993, Grimshaw 1995, Grimshaw 
 

& Samek-Lodovici 1995). The analysis also predicts the universal ban 
 

on overt expletives in null subject languages. 



	A similar result is pursued with respect to agreement, which is 
 

derived by means of three general agreement constraint-schemata.
 

	Finally, the position of subjects and their case assignment 
 

configuration in Italian declaratives, gerundives and subjunctives 
 

are derived from the interaction between CaseGov, a constraint 
 

requiring case assignment under proper government, and the other 
 

constraints of UG. Once reranked, the same constraints derive 
 

declaratives in Arabic and infinitivals with overt subjects in 
 

English and Portuguese, with no appeal to a parametric account of 
 

abstract case assignment.



	Crucially, the analysis of crosslinguistic variation consistently 
 

turns out to be closely tied with the analysis of language-internal 
 

variation, as predicted by an Optimality Theoretic approach to Syntax.