NP arguments cannot be paraphrased by a copular relative clause (examples b and b'), while adjuncts can (examples a and a').
a) a man from Paris a') a man who was from Paris b) the weight of the cow b') *the weight that was of the cow the probability that a PP is an adjunct can be approximated by the probability of its occurrence following a copular verb, such as be, become, appear, seem, remain (Quirk et al., 1985), as indicated in (3).