'Words or Rules' cannot exploit the regularity in exceptions.

succinctly restate their position that the English past tense is governed by two competing mechanisms, identified as 'words and rules', and taken as examples of distinct procedural and declarative systems. Their mechanisms work separately, so that only one or the other is responsible for yielding a particular past tense form. To produce the past tense of keep, words and rules race to generate a response; as the correct past tense of keep is not regular, it must be generated by the lexical mechanism. For this reason, we think of their approach as the 'words or rules' theory. Our approach is different. An integrated connectionist network maps from the stems of all verbs to their past-tense forms, using a single network of units and connections. For example, in the original Rumelhart and McClelland model [2], the same units and connections that produce regular past tenses from regular stems also process the irregulars, so the network has an inherent tendency to do the same thing to the exceptions that it does to regulars – namely, copy the features of the stem to the past-tense form and add /d/, /t/ or /^d/ depending on the final consonant. To produce kept instead of keeped (note that both end with unvoiced /t/) all that is required is to adjust the activations of the output units representing the vowel, something that the network will have learned to do on the basis of experience with keep and its neighbors creep, leap, sleep, sweep and weep. The network uses the same connection-based knowledge that allows it to perform the regular mapping, and also taps into specific connections activated by the particular properties of keep to produce the vowel adjustment. A core difference between these approaches is that one exploits the regularity in the exceptions – what we call quasi-regularity – and the other does not. Quasi-regularity is the tendency for an exception to exhibit aspects of the regular pattern [3]. If there were only a few quasi-regular items, one might treat them as accidents, but in fact nearly all exceptional past-tenses in English are quasi-regular to some extent. To demonstrate this, we will review the different types (for other taxonomies, see [4,5]). (1) Two very frequent verbs, have and make, delete a consonant and add the regular /d/ to what remains, forming had and made. (2) The-eep words listed above and others, including say, do, tell, sell, hear, …