WesterParse: A Transition-based Dependency Parser for Tonal Species Counterpoint

This article describes the syntax parser that is a principal component of WesterParse, a software program designed to evaluate tonal species counterpoint in the version developed by Peter Westergaard (1975). The parser produces interpretations of the pitch-syntactic structure of simple tonal lines. The parser is written in Python and relies on the music21 toolkit. Given a simple tonal line of the sort found in Westergaardian counterpoint, the parser can evaluate its structure and report whether the line is valid. To do so, the parser compiles a set of possible syntactic interpretations. If asked, the program can display the interpretations in a notation program such as MuseScore. (A separate component of WesterParse is a voice-leading evaluator that can test the counterpoint of both simple and combined species for compliance with Westergaard’s rules of voice leading.) After providing a synopsis of Westergaard’s definition of simple tonal lines, the article describes the architecture of the software parser, the scanning process, and the central concept of dependency relations. The parsing operation is then illustrated using Fux’s Dorian cantus firmus, and a closer look is taken at the process for parsing transitions.