This chapter focuses on the internal structure of the lekton. It traces the critical development of the notion of a sentence from Plato’s ‘shortest logos’ in the Sophist with minimal parts, a mainstay in the Platonic and Peripatetic tradition, to the Stoic perspective focused on the notion of completeness: complete is all that is necessary to get one lekton said, however many words or parts of speech may be required to do so. This debate was appropriated, and its different strands merged by the ancient Grammarians. The Stoic influence in the establishment of the discipline is brought out in the discussion. Completeness leads to considerations of incompleteness. The different kinds of complete lekta (questions, commands, exclamations) are tested against a standard of completeness by stripping away different elements to discover that there is a constant axiōmatic core within each kind. A final discussion of the relation of the katēgorēma to the case-ptōsis unfolds into an analysis of the ptōsis as nothing other than forever dependent on a katēgorēma, with no status in itself, but ensconced in a web of relations between concepts in our mind, the hybrid case-bearer (tunchanon), and the external object. Problem cases such as the conundrum of the perishing lekton and the parakatēgorēma are examined in the light of previous claims.