The points I argue here are (i) that elements of phonological universals are conceptually necessary and (ii) that the principle of Full Interpretation (FI) operates at the interface of the articulatoryperceptual module. I assume a generalized autosegmental operation of Merge and Erase, which are fed by the operation Select for syllable structure formation. The whole phonological system is governed by two principles: (i) Underspecification and (ii) FI. The paper argues that the reference to derivational content contributes to the overall generalization in universal phonological inventories and to the optimal localization of descriptive content in the phonologies of individual languages.