A number of studies report that frequency is a poor predictor of acceptability, in particular at the lower end of the frequency spectrum. Because acceptability judgments provide a substantial part of the empirical foundation of dominant linguistic traditions, understanding how acceptability relates to frequency, one of the most robust predictors of human performance, is crucial. The relation between low frequency and acceptability is investigated using corpus- and behavioral data on the distribution of infinitival and finite "that"-complements in Polish. Polish verbs exhibit substantial subordination variation and for the majority of verbs taking an infinitival complement, the "that"-complement occurs with low frequency (<0.66 ipm). These low-frequency "that"-clauses, in turn, exhibit large differences in how acceptable they are to native speakers. It is argued that acceptability judgments are based on configurations of internally structured exemplars, the acceptability of which cannot reliably be assessed until sufficient evidence about the core component has accumulated.