Homophone intrusions in the spelling of regularly inflected Dutch verb forms are used to address a central question in psycholinguistics – and cognitive science in general: do people rely on symbolic mental rules or on a knowledge base that captures the co-occurrence probabilities in the learning domain (statistical learning)? Earlier findings in our research group indicated an effect of homophone dominance in the pattern of intrusion errors when spelling homophonic verb forms: such errors occur more often when the target is the lower-frequency homophone and the intruder the higher-frequency homophone. This is compatible with a statistical learning view but cannot reject a rule-based account enriched with a frequency-sensitive mechanism. To disentangle the two accounts we will compare error patterns in the lexical and sublexical domains. An effect of homophone dominance at the sublexical level cannot be explained by a rule model. Errors in the lexical and sublexical domains will be studied in spelling and reading tasks. Finally, we will attempt to simulate the experimental patterns with two types of computational models: a symbolic model, using morphemes and rules, and a memory-based model, storing whole word forms only and using a similarity metric that can ‘discover’ patterns in its memory store. Together, the experimental and simulation data should enable us to formulate an answer to the question about mental rules.