Superlatives, partitives and apparent φ-feature mismatch in Spanish

Adjectival superlatives in Spanish are expressed by a definite determiner and the com-parative morpheme m ́as ‘more/-er’ modifying the adjective. While gender and numberconcord between the determiner, adjective and noun is generally obligatory, there is asubset of cases where it seems to be disrupted: the determiner surfaces as the so-calledneuter lo, the adjective spells out masculine and there is no overt noun. I argue that thisnon-canonical pattern is the result of a failed Agree dependency between probes on D anda noun underspecified for φ. Failure to value the probe triggers the emergence of defaultsat the point of Vocabulary Insertion: lo and masculine morphology on the adjective. Theanalysis that lo as genderless and numberless receives support from coordination patterns.