After a brief survey of the perception of morphological change in the standard works of the Hispanic tradition in the 20th century, the author first attempts to refine concepts such as analogy, leveling, blending, contamination, etc. as they have been applied to Spanish. He then revisits difficult problems of Spanish historical grammar and explores the extent to which various types of morphological processes may have operated in a given change. Selected problems are examined in light of abundant textual evidence. Some include: the resistance to change of Sp. dormir 'to sleep', morir 'to die', the vocalic sequence /ee/, the reduction of the OSp. verbal suffixes -ades, -edes, -ides, -odes, and the uncertain origin of Sp. eres 'you are'. Important notions such as the directionality of leveling, phonological vs. morphological change in the nominal and verbal paradigms, the morphological spread of sound change, and the role of morphological factors in apparent syntactic change are discussed.