This paper argues that roots can lexically encode grammatically relevant semantics, and that these privileged components of meaning are just those elements of meaning which are also encoded in or directly interact with functional structure. Roots and functional structure then share a limited vocabulary which serves as the interface between conceptual structure and grammatical structure, monitoring the match between them. The supporting case study contrasts the aspectual behavior of degree achievement verbs and locative stative verbs represented by the verb cover. Verbs in both classes are argued to have a stative root at their core and also have stative, inchoative and causative variants. Nonetheless, the inchoative and causative variants of degree achievements have stative and eventive interpretations, while the corresponding variants of cover verbs have only an eventive interpretation. These differences can be explained by the hypothesis that degree achievements have scale structure lexically encoded in the root, while the roots of cover verbs lack such scalar structure. Degree achievements measure the difference in degree to which a scalar property holds of the same individual at two points along an axis in some (possibly non-temporal) domain are derived from the comparative form of the base adjective by a verbal operator which binds the comparandum argument (the standard of comparison) to the argument the verb is predicated of to ensure that the degrees being compared hold of the same individual. Cover verbs are not derived by this operator since they do not have the requisite lexicalized scale, and the inchoative/causative variants are derived differently. Only a theory which assumes that lexically encoded scale structure interacts with functional structure can account for these contrasts.