Up to this point we’ve talked about morphological rules for affixation, compounding, internal stem change and other means of creating new words, but we have only characterized those rules informally. One of the important parts of modeling the mental lexicon is to characterize morphological rules formally. In this section we will look at different formal systems for characterizing morphological rules and try to see how they make different claims about the sorts of morphology we ought to find in the languages of the world.

Morphemes as lexical items: Item and arrangement morphology

Let’s take another look at one of the informal rules of word formation that we proposed.

One way of making this sort of rule formal is to assume that in our mental lexicons the morpheme -ize has a lexical entry, just as free morphemes do, and that part of its lexical entry is the following:

The first line of this rule gives structural information: it says that -ize is a suffix that attaches to nouns or adjectives, and produces verbs. In fact, it says somewhat more than this, as the brackets indicate that when the suffix is added, a bit of hierarchical structure is formed:

The second line of the rule tells us what the resulting word means; this part of the rule can be formalized as well, using special notation, but we will not do so here. We’ll merely say that when the piece -ize is added to a base, it also adds the meaning ‘make A or make/put into N’. Finally, the third line uses the Greek letter sigma (σ) to stand for ‘syllable’, and the subscript W to stand for a ‘weak’ or unstressed syllable. This, then, encodes the information that -ize requires a base that has at least two syllables, the last of which must not bear stress.

This kind of theory in effect makes a claim that affixes are just like free morphemes in that they have lexical entries that include various types of information. The only difference between the entry for an affix and for a base is that the affix is a bound morpheme, and therefore as part of its structural information requires another category to attach to. Theories that propose rules of this sort are traditionally referred to as Item and Arrangement (IA) theories, because they claim that morphemes have independent existence in the mental lexicon with their own structural, semantic, and phonological information, and that they can be arranged hierarchically into words.