Language structure is shaped by communicative needs. This is borne out in Unexpressed Subjects in English: An Empirical Analysis of Narrative and Conversational Discourse, in which Amy M. Lindstrom challenges previous assumptions of what is grammatically possible in English by examining contexts in which speakers omit subjects.
It is generally assumed that inflected verbs in English are always accompanied by overt subjects. However, a corpus-based analysis of interactive conversation and monologic narrative reveals that several variables contribute to a rigorous account of subject (un)expression in spoken American English. These include the discourse/pragmatic factors of accessibility and chronological ordering, the prosodic effect of linking, the mechanical effect of priming, and the semantic factor of verb class. Higher degrees of linking, cohesion, and connection lead to higher instantiations of unexpressed subjects.
Lindstrom demonstrates that unexpressed subjects in English warrant attention as a deliberate, strategic device in discourse, where patterns of distribution challenge the assumption that subject expression is obligatory as an innate grammatical rule.