This paper is a defense of substantive explanations in semantics. I begin by offering a diagnosis of why the view that semantic theories are merely descriptive has been widely accepted in philosophy and I suggest that these grounds are not compelling. Then I argue that semantic explanations don’t have a uniform direction – upwards or downwards the syntactic tree. There is an explanatory division within the lexicon: the meanings of content words (nouns, verbs, adjectives, and adverbs) are semantically fundamental, while the meanings of function words (auxiliaries, connectives, copulas, derivational morphemes, determiners, expletives, prepositions, etc.) are derivative.