Editing Distributed morphology (section)

===Allomorphy===

A core idea in deriving allomorphy in Distributed Morphology is underspecification. Verbal agreement in the present tense in English takes the form /-s/ in the 3rd person singular (‘ex. John eats bologna’), and /Ø/ in all other cases (‘I eat bologna;’ ‘They eat bologna’). The phonological exponents of the feature bundle terminal nodes in the syntactic tree are listed in the Exponent List. We can capture the fact that /-s/ has a much smaller distribution than /Ø/ using the following entries in the Exponent List:

#[3sg, present] ↔ /-s/
#[present] ↔ /Ø/

/-s/ will be inserted whenever its full featural specification is met. In all other cases in the present tense however, such as [2sg, present] or [1sg, present], /Ø/ will be inserted. This is a use of underspecification, the idea that there is a ‘default’ morpheme that is inserted in the general case, and more specific morphemes that are inserted in more specific cases, when their featural specifications are met. In the above example, /Ø/ is underspecified in the sense that it is not specified for person. Underspecification relies on the ‘Maximal Subset Condition.’ <ref name="ReferenceA"/>

The Maximal Subset Condition states firstly that, for a given exponent E to be inserted into some feature bundle T, the featural specification on E must be a subset of the features on T. In this way, /-s/ is not a possible exponent for a feature bundle [2sg, present]. However, /Ø/ is a possible exponent for the feature bundle [3sg, present]. To ensure that /-s/ is chosen over /Ø/ for the bundle [3sg, present], the Maximal Subset Condition states secondly that, between two exponents E and F which both contain a subset of the features in a feature bundle T, the exponent that contains the maximal subset of the features in T will be selected.

Featural specification derives allomorphy in featural paradigms. Allomorphy in which different phonological exponents of the same feature bundle are idiosyncratically realized depending on the morphological or phonological environment is captured through contextual specification. An example of such allomorphy is the English plural marker. The typical English plural marker is /-z/, as in bulls. However, the plural of child is children, and the plural of cactus is cacti. Since the choice of the plural morpheme exponent is not related to features, but rather simply to the root it attaches to, the roots must be listed in the contextual specification:
#[-sg] ↔ /-z/
#[-sg] ↔ /-ren/ / _ {child}
#[-sg] ↔ /-i/ / _ {cact}

If the contextual specification of some item is met, it is inserted. Otherwise, insert the item that has no contextual specification. This is an example of the ‘elsewhere condition’.<ref name="ReferenceA"/> Note that the Maximal Subset Condition stated above is a formal instantiation of the elsewhere condition.

Contextual specification is also used to account for phonologically conditioned suppletive allomorphy, using phonological contexts. Thus, the singular indefinite marker in English can be stated as follows (we could also underspecify one of the allomorphs to express a default morpheme):

#[-def, +sg] ↔ an / _V
#[-def, +sg] ↔ a / _C

A prediction about suppletive allomorphy in Distributed Allomorphy is that, assuming exponents are inserted in a bottom-up fashion of the syntactic tree, it should always be ‘inward-looking.’ This means that contextual allomorphy can only involve the selection of an allomorph based on something lower in the tree. That is, the contextual environments must always involve items lower in the tree.

Morphologically conditioned allomorphy may involve [[suppletion]] (as in ''go-Ø/wen-t'') or readjustment rules that apply in the context of certain Vocabulary items (as in ''buy-Ø/bough-t'').  Suppletion and readjustment rules apply to a terminal node and its associated Vocabulary item – unlike affixation, which combines this terminal node with a separate terminal node that has its own distinct (though potentially null) Vocabulary item.  Suppletion arises from the competition of Vocabulary items for insertion into a terminal node.  Competition involving root Vocabulary items is a topic of ongoing research, however.  Early work in Distributed Morphology suggests that a single, abstract lexical root appears in the syntax; in this view, roots do not compete for insertion into root nodes, but exist in free variation, constrained only by semantic and pragmatic well-formedness.  Subsequent research has suggested that the distribution of root Vocabulary items can be grammatically restricted (Embick 2000, Pfau 2000, Marantz 2013); this means that roots may be featurally restricted and thus subject to competition.  The issue of whether root alternations such as ''buy-Ø/bough-t'' are better handled by suppletion or readjustment rules remains a topic of debate (Embick & Marantz 2008, Siddiqi 2009, Bonet & Harbour 2012).

The term ''suppletion'' refers to allomorphy of an open-class lexical item. For a large-scale study of suppletion in the context of comparative and superlative adjectival morphology within the general framework of Distributed Morphology, see Bobaljik (2012).<ref name=":0">Bobaljik, Jonathan David (2012). Universals In Comparative Morphology: Suppletion, Superlatives, and the Structure of Words. Cambridge, MA: MIT Press.</ref>