This chapter claims that phonology is like syntax in that the input consists of lexical items with little or no structure. Specifically, we argue that metrical foot structure is always absent from underlying representations. This argument is framed in a derivational version of Optimality Theory called Harmonic Serialism (HS). The natural assumption in HS is that metrical structures are built one foot at a time. This mode of structure building has desirable consequences for locality in stress patterns. But these results can be subverted if structures that the grammar cannot produce are already present in underlying representations. The chapter concludes with a further phonology-syntax parallel: exceptional stress patterns require uninterpretable features whose presence can influence the structures that are built.