In generative linguistics, Distributed Morphology is a framework for theories of morphology introduced in 1993 by Morris Halle and Alec Marantz. The central claim of Distributed Morphology is that there is no unified Lexicon as in earlier generative treatments of word-formation. Rather, the functions that other theories ascribe to the Lexicon are distributed among other components of the grammar.
In Distributed Morphology, the abstract morphemes that comprise words are held to be completely empty of phonological information until after the syntactic component has finished manipulating them. That is, the structure of the sentence is worked out before there are any actual words present. The pieces of words that best match the syntactic structure are then inserted into the sentence.
There is no central repository of Saussurean signs in the model, in which morphological, syntactic and semantic information is collected in discrete lexeme-like bundles. Instead, one repository ('List 1") contains the abstract syntactic formatives, and is input to the syntax. Another ('List 2') provides the phonological content for List 1 elements in syntactic context—these are called 'Vocabulary Items—and a third, ('List 3', sometimes also called the Encyclopedia) provides semantic content for List 1 elements in syntactic context.
Core properties 
There are three main properties which distinguish Distributed Morphology from other theories:
- Late Insertion
- Phonological information is inserted into syntactic structure only after all syntactic operations have applied.
- Underspecification of Vocabulary items
- The phonological string inserted in a given syntactic position does not necessarily have to be specified for all of the morphosyntactic features of that position.
- Syntactic Hierarchical Structure All the Way Down
- The relationships among elements within words are structurally identical to those relationships that hold among words.
Vocabulary items 
Distributed Morphology makes a distinction between the notion of a morpheme, which refers to a syntactic terminal element, and that of a Vocabulary item, which is defined as a relation between a string of phonological information and the context in which this string may be inserted. The standard schema for the representation of a Vocabulary item is as follows:
- signal ↔ context of insertion
An example Vocabulary item, from English:
- /-d/ ↔ [+past]
The functional vs. lexical distinction 
The division between closed and open word classes is recast in Distributed Morphology  as the distinction between f-morphemes (traditional closed classes) and l-morphemes (traditional open classes), which are defined as follows:
- A Vocabulary item whose context of insertion is sufficient to determine its phonological form.
- A Vocabulary item whose phonological form cannot be determined solely by its context of insertion. This includes the traditional classes of nouns, adjectives, and verbs. These are often also referred to as 'Roots'.
For example, to create the sentence, The dogs ate the meat, the word dogs is inserted after a noun root with the meaning [DOG] combines with a feature [plural]. At the end of the derivation, the English word dogs is inserted in the appropriate spot - that is, where the syntax decides to place the subject. Also, a verbal root meaning [EAT] combines with a [past tense] feature and [3rd person plural] feature. The closest matching word in English is ate, which is inserted wherever the syntax has determined that the verb should go. We should note that the [3rd person plural] feature is not actually matched in English, because there is a total lack of person/number agreement in the past tense in English:
|I ate||we ate|
|you ate||you ate|
|s/he ate||they ate|
Of course, many other languages do have active person/number agreement that must be matched. Consider the same verb conjugated in the past tense in European Portuguese:
|eu comi||nós comemos|
|tu comeste||vós comestes|
|ele/ela comeu||eles/elas comeram|
Thus, the same sentence in Portuguese would enter the verb comeram, since it is the best match for the combination [EAT] [past tense] [3rd person plural]. The words cannot be entered until the features are combined in the right way. Insertion of phonological exponents is governed by the Subset Principle, the following version of which is from Halle (1997):
The phonological exponent of a Vocabulary Item is inserted into a morpheme in the terminal string if the item matches all or a subset of the grammatical features specified in the terminal morpheme. Insertion does not take place if the Vocabulary item contains features not present in the morpheme. Where several Vocabulary items meet the conditions for insertion, the item matching the greatest number of features specified in the terminal morpheme must be chosen.
Phonologically-conditioned allomorphy is handled in terms of contextual specification on Vocabulary items. For example, the allomorphs of the Moroccan Arabic 3rd person singular masculine object clitic could be specified as follows:
- /-h/ ↔ [-author,-participant, -pl, -fem] / V __
- /-u/ ↔ [-author,-participant, -pl, -fem] / C __
The underscore ___ above indicates that these Vocabulary items can only be inserted when they meet the environment specified.
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).
Morphological operations 
Distributed Morphology recognizes a number of morphology-specific operations. Among the most widely employed within the theory are impoverishment, fission, and fusion.
'Impoverishment' (a term introduced into the theory in Bonet 1991) refers to a change in the feature content on a terminal node prior to Vocabulary Insertion, resulting in a less marked feature content. This can be accomplished by deleting a feature or by changing it from a marked to an unmarked value (e.g. [+plural] to [-plural]). Impoverishment accounts for cases in which spellout of a terminal node by a featurally specific Vocabulary Item is blocked by a less specific Vocabulary Item.
Impoverishment can also target an entire terminal node (rather than just one of its features), in which case it is referred to as 'obliteration'. This results in the complete absence of the morpheme from the structure of the word.
Fusion refers to the combination of two distinct terminal nodes into a single node prior to Vocabulary Insertion.
Fission refers to the splitting of one terminal nodes into two distinct terminal nodes prior to Vocabulary Insertion. Some of the most well-known cases of fission involve the imperfect conjugations of Semitic, in which agreement morphology is split into a prefixal and suffixal part, as investigated in the work of Noyer (1992).
As the primary competition among Vocabulary items is governed by the Subset principle, which determines the greatest number of matching features among competing items, a great deal of research in Distributed Morphology is devoted towards determining what constitutes the exact set of features employed within the Morphological Component. The majority of this research focuses on the inflectional features of person, case, number, and gender.
- Harley and Noyer (1999)
- Harley and Noyer 1999:5
- Halle and Marantz 1993:126
- Harley and Noyer 1998
- Arregi and Nevins 2007
Marantz, Alec (1997), "No Escape From Syntax: Don’t Try Morphological Analysis in the Privacy of Your Own Lexicon", University of Pennsylvania Working Papers in Linguistics (Philadelphia, Pennsylvania: Upenn Department of Linguistics)
Embick, David; Noyer, Rolf (2007), "Distributed Morphology and the Syntax/Morphology Interface", The Oxford Handbook of Linguistic Interfaces (Oxford, UK: Oxford University Press): 289–324
Bobaljik, Jonathan David (2012). Universals In Comparative Morphology: Suppletion, Superlatives, and the Structure of Words. Cambridge, MA: MIT Press.
Bonet, Eulàlia (1991). Morphology after Syntax: Pronominal Clitics in Romance. PhD dissertation, MIT. Distributed by MIT Working Papers in Linguistics.
Arregi, Karlos; Andrew Nevins (2007). "Obliteration vs. Impoverishment in the Basque g-/z- Constraint". Proceedings of the 26th Penn Linguistics Colloquium, Penn Working Papers in Linguistics 13 (1): 1–14.
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