I hope to have made it clear both why productivity is a notion that must be approached cautiously, and how it is possible to untangle its various aspects. The most important findings to bear in mind are two. First, a process can be formally regular without being semantically regular, as is illustrated by the suffixation of -ion to produce nouns from verbs with the root -mit. Secondly, semantically regular relationships between lexemes (that is semantic relationships that have more or less widespread parallels involving other lexemes) can subsist without morphological support, as is illustrated by the terms for domestic animals at (2). If semantic and formal regularity often go together, that is hardly surprising, since lexemes so constructed will be relatively easy to learn and will provide the most natural models on which new lexemes can be created; but it is oversimplifying to classify as simply ‘irregular’ or ‘unproductive’ any morphological relationship that is not in all respects straightforward.

It is natural to ask why productivity crops up as an issue so insistently with word formation but not with sentence formation. Are there no syntactic constructions that are less productive than others? Such constructions do indeed seem to exist. For example, there is no obvious reason why the construction illustrated at (6), in which a verb has two objects, should be acceptable in those examples but unacceptable (or less readily acceptable) in the examples at (7):

(6) a. They gave us a present.

      b. They faxed us the answer.

      c. They allocated us two seats.

      d. They baked us a cake.

(7) a. *They donated us some pictures.

      b. *They yelled us the instructions.

      c. *They planned us a holiday.

      d. *They spoiled us the evening.

Seemingly, the lexical entries for at least some of these verbs must specify whether or not they tolerate the double-object construction. The reason why this sort of syntactic restriction is less usual than the kind of morphological restriction is not immediately obvious. It may simply be that the propensity for words (i.e. lexemes) to become lexical items, and thus to acquire idiosyncrasies, inevitably compromises the generality of the processes whereby complex words are formed (that is, processes of derivational morphology and compounding); on the other hand, the propensity for phrases to become lexical items is relatively weak. But why should this difference in propensity for lexical listing exist, given that wordhood is neither a necessary nor a sufficient condition for lexical-item status? A plausible answer is that shorter items are more likely to be lexically listed than longer items are, and words (even complex words) are generally shorter than phrases.