Abstract
Harmonic word order is a well-established tendency in natural languages, which has previously been explained as a single ordering rule for all head-dependent relations. We propose that it can be more parsimoniously explained as an outcome of word-class frequencies, where the purported "head" is the most frequently instantiated word class in a phrasal schema. We show that the most frequent class gravitates spontaneously to an edge position in a phrasal replication process, as long as words of one class may influence the position of words of another class. This avoids the need to posit head-dependent ordering as an innate rule or bias, simplifying our theory of word order. We demonstrate the spontaneous emergence of harmony from word-class frequencies using a simple computational model of phrasal replication, and in further extensions show that the principle remains robust with fuzzy word classes and multiword chunks, can capture competition between harmony and locality, and is compatible with the results of behavioral experiments on harmonic ordering. Our findings support further exploration of syntactic models with nondiscrete word classes.