We develop a large set of pseudowords that systematically varies length and phonotactic probability and obtain acceptability ratings using an online interface. We find that phonotactic likelihood and the presence of an apparent morphological parse both significantly predict acceptability; pseudowords containing known morphemes are more acceptable than otherwise comparable pseudowords that do not. We find support for the conjecture that novel words with apparent morphology are advantaged as additions to the lexicon. The resulting lexicon, as observed, is one in which long words are not a random sampling of phonotactically acceptable wordforms, but instead tend to be completely or partially decomposable into morphemes.