How sensitive are adults to the role of morphology in spelling?

In English, the letters in a word’s spelling are sometimes associated with its part of speech or morphological structure. For example, final /ɨk/ and /ɨs/ are almost always spelled as ‹ic› and ‹ous›, respectively, when they are adjectival suffixes (e.g., basic, callous). In words that are not adjectives, these endings are likely to be spelled in other ways (e.g., gimmick, callus). These associations are rarely taught explicitly, but have adults internalized them using their implicit statistical learning skills? We studied this issue by having adults write sentences in which nonwords with final /ɨk/ and /ɨs/ served as either adjectives or nouns. Participants used spellings with final ‹ic› and ‹ous› more often when the nonwords appeared in adjective contexts than in noun contexts. This effect was stronger in participants who performed better on a standardized test of spelling ability than in participants who scored less well. However, the difference between the two contexts was substantially smaller than expected based on the statistics of the English writing system. The results point to the limits of statistical learning for certain potentially helpful morphological patterns. People may need explicit instruction in order to benefit fully from the regularities that English spelling offers.