In the literature on the representation and processing of language there is a debate between connectionist-based single-mechanism and symbolic-based dual-mechanism models. One of the main points of discussion is whether symbolic procedures (such as conjugational class) or associative memory procedures (e.g., based on rhyme) are operative in mental representation. This paper reports the results of two experiments testing the mental representation of Spanish Present Tense and Spanish Past Imperfect novel (made-up) verbs belonging to different conjugational classes (e.g. vantar, tonder). Native Spanish participants were asked to inflect novel verbs in sentence contexts to see whether they inflected the verbs based on abstract symbolic features or on phonological similarity to other verbs. The conclusions of this study are: (a) conjugational classes are not mere descriptive generalizations, but play a relevant role in the organization of verbs in speakers' minds, (b) an associative memory based on phonological similarity is also operative, but in restricted domains, and (c) two different systems (one based on the manipulation of abstract categories and one associative memory type of system) are required to account for the representation and processing of Spanish verbal morphology, thus supporting the dual system perspective.