GERMAN INFLECTION - THE EXCEPTION THAT PROVES THE RULE

Language is often explained as the product of generative rules and a m emorized lexicon. For example, most English verbs take a regular past tense suffix (ask-asked), which is applied to new verbs (faxed, wugged ), suggesting the mental rule ''add-ed to a Verb.'' Irregular verbs (b reak-broke, go-went) would be listed in memory. Alternatively, a patte rn associator memory (such as a connectionist network) might record al l past tense forms and generalize to new ones by similarity; irregular and regular patterns would differ only because of their different num bers of verbs. We present evidence that mental rules are indispensible . A rule concatenates a suffix to a symbol for verbs, so it does not r equire access to memorized verbs or their sound patterns, but applies as the ''default,'' whenever memory access fails. We find 21 such circ umstances for regular past tense formation, including novel, unusual-s ounding, and rootless and headless derived words; in every case, peopl e inflect them regularly (explaining quirks like flied out, sabre-toot hs, walkmans). Contrary to the connectionist account, these effects ar e not due to regular words constituting a large majority of vocabulary . The German participle -t applies to a much smaller percentage of ver bs than its English counterpart, and the German plural -s applies to a small minority of nouns. Bur the affixes behave in the language like their English counterparts, as defaults. We corroborate this effect in two experiments eliciting ratings of participle and plural forms of n ovel German words. Thus default suffixation is not due to numerous reg ular words reinforcing a pattern in associative memory. Because defaul t cases do not occupy a cohesive similarity space, but do correspond t o the range of a symbol, they are evidence for a memory-independent, s ymbol-concatenating mental operation. (C) 1995 Academic Press,Inc.