Some of the patterns we have looked at in earlier chapters can be described in terms of a word formation rule of the kind outlined by Aronoff, in which both the base of a complex word and the complex word itself are specified in terms of their category and meaning. With prefixation by pre-, mis-and (generally) re-(3.2) for example, it is necessary to specify only that the bases are verbs, and that prefixed verbs are 'accomplishments'. -en attaches exclusively to monosyllabic adjective bases to form verbs (sweeten), and -ive to verb bases ending in [s] or [t] to form 'subjective' adjectives (replacive, pollutive). According to the 'unitary base hypothesis', a word formation rule 'will never operate on either this or that'! (Aronoff 1976, 48), and its output is predictable. But rules, or patterns, are not always so concisely definable, and the forms they are perceived to take will depend on the relative importance we may attach to phonology, to the syntactic relationship between base and complex word, and to meaning.