This study seeks to determine the relative position of derivational affixes on the lexicon-grammar continuum in English. Its major claim is that the set of prefixes is rather more lexical and the set of suffixes rather more grammatical in nature. This hypothesis is supported by a battery of ten tests (nine linguistic and one psycholinguistic). All tests converge to the point where we can raise the possibility of a unified explanation. A theoretical account is offered which is grounded in both language structure and processing. It is erected on a temporal asymmetry between prefixes and suffixes and a logical (relational) asymmetry between stems and affixes. In conjunction with the immediacy-of-processing assumption, these asymmetries lead to a temporal precedence of (more) lexical over (more) grammatical material, hence the higher lexicalness of prefixes and the higher grammaticalness of suffixes. An extended focus on inflectional morphology locates inflectional suffixes at the grammatical end of the spectrum. Inflectional prefixes in languages other than English may find a place either between derivational prefixes and derivational suffixes or between derivational and inflectional suffixes.