Pinker and Prince postulate a dual-route model of linguistic knowledge, according to which the ability to transform verbs into the past tense consists in either:
- "following a rule (add "-ed" to the verb—eg "guide" becomes "guided"), or
- consulting a list of exceptions (e.g. "run" becomes "ran", "weep becomes wep"t, etc).
But any system can be described in this way, because a set of rules only has to fit some cases, with the rest being treated as exceptions.
Such an approach is "
like saying that all of the observations in my experiment fit a particular hypothesis except the ones that I’ve decided to exclude (p.94)."