This dissertation approaches the idea of lexical types such as word, clitic and affix from an oblique angle. Starting with Cardinaletti & Starke's (1999) diagnostics for the Weak Pronoun, I deconstruct the category of clitic, breaking it down into two binary qualities: the syntactic primitive of being linked to a head of a different basic phrasal category, and the phonological primitive of being internal to the phonological word of the host. I argue that the syntactic behaviors of clitic-words, in particular pronominal clitic-words, are predictable if we assume that there is an operation that allows Xmin/max elements to fuse with X0 nodes during a syntactic derivation. This creates a complex X0 node that selects a clitic-type spell-out form. This fusion process—m-merge, adapted from Matushansky (2006)—is the same process that drives the incorporation part of head-movement. I also propose that the features identified as phonologically clitic-like—reduction, lack of a syllabic nucleus, no coordination and morphological simplicity—result from a similarity to inflectional affixes. Instead of arguing for a distinct clitic phonology I suggest that clitics—when they are simple feature bundles—and agreement affixes are functionally identical and therefore are likely to undergo spell-out in the same way, in particular by being realized internally to their hosts' phonological word, and being able to determine the shape of their host to a greater extent than we expect word-level phonological processes to allow. The evidence supporting these claims shows that many strange grammatical phenomena can be explained simply if we adopt the above principles. The operation m-merge—fusing an Xmin/max to an X0 node—offers a straightforward account of the WH as C pattern in interrogative relatives in Middle Bavarian and Lake Constance Alemannic. Considering how my model affects the diachronic trajectory of word-to-clitic-to-affix and adopting a restricted version of Roberts (2010) Move via Agree provides insight into the behavior of French subject pronouns in Old French, Standard French, and Contemporary Colloquial French. Most dramatically, my model offers a straightforward analysis for eight highly distinct types of φ marking in Middle Welsh, even to the point of predicting that three very different syntactic contexts will have the same realization for a φ-marked element. In sum, I argue that although clitics look and behave quite differently from canonical independent words and inflectional affixes, with a thorough understanding of the operations underlying head-movement and vocabulary insertion for paradigmatic elements, clitics are a predicted part of the model. Instead of requiring extra apparatus to explain, clitics offer us ways of simplifying our approach to syntax and the syntax-morphology interface as a whole.