Optional agreement as successful/failed Agree

We investigate optional predicate agreement in Santiago Tz’utujil (Mayan). Several generalizations emerge: (i) inanimate arguments base-generated as complements control agreement optionally; (ii) some animate arguments base-generated as complements control agreement optionally; (iii) all arguments base-generated as specifiers control full agreement obligatorily. We propose that two conditions must be met for the operation Agree to succeed, resulting in the exponence of all the features of the agreement controller. First, a goal must be visible (bear the right feature). Second, a goal must be accessible (be in the right structural position). If one or both conditions are not met, Agree fails, but the derivation converges and 3sg agreement is exponed. While Agree is deterministic, surface optionality arises when the operation fails. We use optional agreement to diagnose the syntactic structure of understudied constructions in Mayan (nominalizations, Agent Focus). We discuss microvariation, highlighting methodological considerations that arise when assuming an I-language approach.