Although L1 French speakers (FS) acquire the formal features of gender and number early, agreement appears to take longer, leading to persistent difficulties even for cases of straightforward agreement within a nominal or verbal phrase. This begs the questions of how adult FSs (n = 168) may fare with idiosyncratic cases of agreement such as nominal affective constructions and past participles as measured by a written grammaticality judgment /correction task and preference/grammaticality judgment task. The findings showing that participants performed better at correctly accepting than rejecting stimuli, are consistent with an increasing number of empirical studies revealing individual differences among adult L1 speakers. The findings are discussed from a generative perspective and the usage-based perspective of the Basic Language Cognition-High Language Cognition theory of L1 proficiency (Hulstijn, 2015).
