Comprehension and production of subject pronouns: Evidence for the asymmetry of grammar Charlotte Koster, John Hoeks and Petra Hendriks 1. Introduction 1 One central property of human language is that, in general, adult speakers can understand whatever they produce and adult listeners can produce whatever they understand. This observed symmetry between production and comprehension might not, however, be an inherent property of gram- mar. It is well-known that children sometimes understand meanings that they do not yet correctly produce. Recent studies have also provided evi- dence that children sometimes correctly produce forms that they do not yet understand. Such delays in comprehension have been found in areas as diverse as object pronouns, indefinite noun phrases, prosody and contras- tive stress, word order and structural attachment (see Hendriks and Koster 2010, for discussion). Many of these delays occur relatively late in acquisi- tion, after age 5 or even later, resulting in a gap between correct production and correct comprehension that can span several years. Such asymmetries in language acquisition present a real challenge to rule-based systems of grammar. If children know a rule of grammar, they should be able to use this rule in production and comprehension alike. So, how can asymmetries between comprehension and production in child lan- guage be explained? Taking object pronouns as an example, previous ac- counts of children’s acquisition have attempted to explain comprehension errors as resulting from a lack of pragmatic knowledge necessary to distin- guish exceptional cases from the standard pattern (Thornton and Wexler 1999), from insufficient working memory capacity for the parser to com- pare alternative forms and meanings (Reinhart 2006), or as an experimental artifact due to an unbalanced context (Conroy et al. 2009). One common denominator in all these accounts is that they fail to provide a detailed ex- planation of children’s successful production of object pronouns. The general solution of arguing that asymmetries arise as a result of dif- ficulties at the interface with other linguistic modules and do not reflect core properties of the grammar also makes it difficult to explain why cer- tain delays occur only in particular syntactic environments or only in par-