In the literature on Null Subject Languages (NSLs) since Rizzi (1982), the three properties that are commonly thought to be connected are (i) the richness of inflectional morphology, (ii) free subject inversion, and (iii) the COMP-trace effect. The connection between them is that if a language (e.g., Italian) has the option of having a null subject (NS) pronominal pro in subject position (i.e., SpecIP) as a result of having rich inflectional (i.e., verbal agreement) morphology, as represented in (1a), then the same element may appear in the same position in cases of subjects occurring postverbally as in (1b) and in cases of long-distance subject extraction where the postverbal trace is properly governed by the verb, as in (1c):

Few topics in the phonological literature have inspired the amount of attention that has been lavished on the notorious “mute-e” of contemporary French. Perhaps the most perplexing difficulty for phonologists is how (or even whether) to include schwa in phonological representations. Solution of the representation problem, moreover, is necessary for a proper identification of the conditions under which schwa is deleted, maintained or inserted, and for an analysis of alternations linking schwa and other vowels. Many different solutions to the representation problem have been suggested: schwa as a distinct vowel; schwa as absent from the phonemic inventory (hence from underlying representations) and inserted as a “lubrifiant”; or (in the current non-linear literature), schwa as an empty nucleus; schwa as an unlinked vowel.