"Assemblage" is a fundamental archaeological construct. By their composition, we interpret assemblages as expressions of activity or cultural identity. Yet they are not simple products of these factors alone but also of formation processes. Assemblages accumulated over varying spans, with varying combinations of tool types and discard rates. They are contexts for the playing out of complex relationships, not static types. This is a materialist view, against the essentialist view that assemblages are exemplars of ideal types (e.g., "base camps," "Quina Mousterian"). Materialism implies that their size and composition, fundamental assemblage characteristics, are correlated variables, not fixed properties, and that composition varies as size increases. I document size dependence consistent with materialism in Paleoindian and Paleolithic assemblages. Among ways to analyze size-dependent assemblage data, I apply "SHE analysis"—the joint study of assemblage richness, heterogeneity, and evenness—to gauge data’s fit to theoretical models. Archaeologists acknowledge size dependence, but we misapprehend it as a methodological bias of assemblage measures that must be suppressed when, in materialist perspective, it reveals meaningful relationships that an essentialist view cannot.