Spanish American plural formation is discussed in relation to attempts that have been made to write a set of phonological rules that would correctly predict the Spanish plural using a combination of phonological rules and word structure constraints. A brief synopsis is resented of why previous attempts to predict the plural are in error. Phonological rules that work for Peninsular Spanish do not work for Latin American Spanish because of a different phonemic inventory. The solution using a combination of phonological rules and word structure constraints optimally minimizes the exceptions, correctly predicts dialect variations, and accounts for all the data without referring to abstract underlying forms or without using extrinsically ordered, opaque, or absolute neutralization rules. (SW)