Acceptability judgments are reports of a speaker’s or signer’s subjective sense of the well-formedness, nativeness, or naturalness of (novel) linguistic forms. Their value comes in providing data about the nature of the human capacity to generalize beyond linguistic forms previously encountered in language comprehension. For this reason, acceptability judgments are often also called grammaticality judgments (particularly in syntax), although unlike the theory-dependent notion of grammaticality, acceptability is accessible to consciousness. While acceptability judgments have been used to test grammatical claims since ancient times, they became particularly prominent with the birth of generative syntax. Today they are also widely used in other linguistic schools (e.g., cognitive linguistics) and other linguistic domains (pragmatics, semantics, morphology, and phonology), and have been applied in a typologically diverse range of languages. As psychological responses to linguistic stimuli, acceptability judgments are experimental data. Their value thus depends on the validity of the experimental procedures, which, in their traditional version (where theoreticians elicit judgments from themselves or a few colleagues), have been criticized as overly informal and biased. Traditional responses to such criticisms have been supplemented in recent years by laboratory experiments that use formal psycholinguistic methods to collect and quantify judgments from nonlinguists under controlled conditions. Such formal experiments have played an increasingly influential role in theoretical linguistics, being used to justify subtle judgment claims or new grammatical models that incorporate gradience or lexical influences. They have also been used to probe the cognitive processes giving rise to the sense of acceptability itself, the central finding being that acceptability reflects processing ease. Exploring what this finding means will require not only further empirical work on the acceptability judgment process, but also theoretical work on the nature of grammar.
The Romance languages are characterized by the existence of pronominal clitics. Third person pronominal clitics are often, but not always, homophonous with the definite determiner series in the same language. Both pronominal and determiner clitics emerge early in child acquisition, but their path of development varies depending on clitic type and language. While determiner clitic acquisition is quite homogeneous across Romance, there is wide cross-linguistic variation for pronominal clitics (accusative vs. partitive vs. dative, first/second person vs. third person); the observed differences in acquisition correlate with syntactic differences between the pronouns. Acquisition of pronominal clitics is also affected if a language has both null objects and object clitics, as in European Portuguese. The interpretation of Romance pronominal clitics is generally target-like in child grammar, with absence of Pronoun Interpretation problems like those found in languages with strong pronouns. Studies on developmental language impairment show that, as in typical development, clitic production is subject to cross-linguistic variation. The divergent performance between determiners and pronominals in this population points to the syntactic (as opposed to phonological) nature of the deficit.
Eve V. Clark
Several factors influence children’s initial choices of word-formation options––simplicity of form, transparency of meaning, and productivity in current adult speech. The coining of new words is also constrained by general pragmatic considerations for usage: Reliance on conventionality, contrast, and cooperation between speaker and addressee. For children acquiring French, Italian, Portuguese, and Spanish, the data on what they know about word-formation for the coining of new words consist primarily of diary observations; in some cases, these are supplemented with experimental elicitation studies of the comprehension and production of new word-forms. The general patterns in Romance acquisition of word-formation favor derivation over compounding. Children produce some spontaneous coinages with zero derivation (verbs converted to nouns in French, for example) from as young as 2 years, 6 months (2;6). The earliest suffixes children put to use in these languages tend to be agentive (from 2;6 to 3 years onward), followed by instrumental, objective, locative, and, slightly later, diminutive. The only prefixes that emerge early in child innovations are negative ones used to express reversals of actions. Overall, the general patterns of acquisition for word-formation in Romance are similar to those in Semitic, where derivation is also more productive than compounding, rather than to those in Germanic, where compounding is highly productive, and emerges very early, before any derivational forms.
Adjectivalization is the derivation of adjectives from a verb, a noun, an adjective, and occasionally from other parts of speech or from phrases. Cross-linguistically, adjectivalization seems to be less frequent than nominalization and verbalization. In most languages adjectivalization involves suffixation, but other adjectivalization devices, such as prefixation, reduplication or zero derivation, are also attested.
Adjectivalization by means of suffixation has been studied in depth for English. As for other languages in which suffixation is used for adjectivalization, topics that have been studied for English are the types of suffixes used for adjectivalization, their productivity, their semantic contribution, the category of the base to which they attach, and their etymology. For English an etymological distinction between native suffixes and suffixes with a Romance, more specifically Latinate, origin can be made, related to their bound or non-bound character, the type of base to which they attach, and the prosody of the derived word.
One of the major challenges to the idea of word-class changing derivation, in this case adjectivalization, comes from polyfunctional words. Participles may function both as verbs and as adjectives, which leads to the question how these complex forms are formally and semantically related. There are also derivational suffixes that are used for the formation of both adjectives and nouns. For these cases as well the formal and semantic relation has to be established. For several Western European languages a relation has been established, in the theoretical literature, between the polyfunctionality of adjectival/nominal suffixes and their influence on the prosody or the phonological properties of the root, due to their etymology. It seems that the dichotomy between two types of suffixes that is created in this way does not always occur and that there is also a mixed case.
Patricia Cabredo Hofherr
Agreement is defined as the systematic covariance of one element with another. The most uncontroversial agreement configuration is that between a controller—an element intrinsically specified for a value of an agreement feature—and the target of agreement—the element reflecting a displaced feature value of the controller. The distribution of morphological agreement markers is however much wider than controller–target configurations: targets can express agreement values for features that are not visible on the controller and even show agreement morphology in the absence of a lexical controller. A second source of variation is due to the fact that in certain contexts there is a choice between syntactic agreement (with formal features of the controller) and semantic agreement (with semantic features of the referent of the controller). The choice between syntactic and semantic agreement is correlated in part with cross-linguistically observed regularities that have been formulated as the agreement hierarchy and the animacy hierarchy.
Agreement morphology harnesses the same morphological devices found with derivation and inflection. Like inflectional morphology more generally, agreement morphology is only present in a subset of the world’s languages.
The American descriptivist movement includes the work of Edward Sapir, Leonard Bloomfield, and their students, including Zellig Harris, Charles Hockett, and Kenneth Pike. Their work on morphology set the stage for much of the discussion of the subject in the years that followed, right up to today. In a number of ways they laid greater emphasis on the role of morphemes in morphological analysis when linguists in Europe focused more on the central role played by words in morphosyntactic paradigms.
Analogy is traditionally regarded as one of the three main factors responsible for language change, along with sound change and borrowing. Whereas sound change is understood to be phonetically motivated and blind to structural patterns and semantic and functional relationships, analogy is licensed precisely by those patterns and relationships. In the Neogrammarian tradition, analogical change is regarded, at least largely, as a by-product of the normal operation (acquisition, representation, and use) of the mental grammar. Historical linguists commonly use proportional equations of the form A : B = C : X to represent analogical innovations, where A, B, and C are (sets of) word forms known to the innovator, who solves for X by discerning a formal relationship between A and B and then deductively arriving at a form that is related to C in the same way that B is related to A.
Along with the core type of analogical change captured by proportional equations, most historical linguists include a number of other phenomena under the analogy umbrella. Some of these, such as paradigm leveling—the reduction or elimination of stem alternations in paradigms—are arguably largely proportional, but others such as contamination and folk etymology seem to have less to do with the normal operation of the mental grammar and instead involve some kind of interference among the mental representations of phonetically or semantically similar forms.
The Neogrammarian approach to analogical change has been criticized and challenged on a variety of grounds, and a number of important scholars use the term “analogy” in a rather different sense, to refer to the role that phonological and/or semantic similarity play in the influence that forms exert on each other.
Japanese is a language where the grammatical status of arguments and adjuncts is marked exclusively by postnominal case markers, and various argument realization patterns can be assessed by their case marking. Since Japanese is categorized as a language of the nominative-accusative type typologically, the unmarked case-marking frame obtained for transitive predicates of the non-stative (or eventive) type is ‘nominative-accusative’. Nevertheless, transitive predicates falling into the stative class often have other case-marking alignments, such as ‘nominative-nominative’ and ‘dative-nominative’. Consequently, Japanese provides much more varying argument realization patterns than those expected from its typological character as a nominative-accusative language.
In point of fact, argument marking can actually be much more elastic and variable, the variations being motivated by several linguistic factors. Arguments often have the option of receiving either syntactic or semantic case, with no difference in the logical or cognitive meaning (as in plural agent and source agent alternations) or depending on the meanings their predicate carry (as in locative alternation). The type of case marking that is not normally available in main clauses can sometimes be obtained in embedded contexts (i.e., in exceptional case marking and small-clause constructions). In complex predicates, including causative and indirect passive predicates, arguments are case-marked differently from their base clauses by virtue of suffixation, and their case patterns follow the mono-clausal case array, despite the fact that they have multi-clausal structures.
Various case marking options are also made available for arguments by grammatical operations. Some processes instantiate a change on the grammatical relations and case marking of arguments with no affixation or embedding. Japanese has the grammatical process of subjectivization, creating extra (non-thematic) major subjects, many of which are identified as instances of ‘possessor raising’ (or argument ascension). There is another type of grammatical process, which reduces the number of arguments by virtue of incorporating a noun into the predicate, as found in the light verb constructions with suru ‘do’ and the complex adjective constructions formed on the negative adjective nai ‘non-existent.’
Malka Rappaport Hovav
Words are sensitive to syntactic context. Argument realization is the study of the relation between argument-taking words, the syntactic contexts they appear in and the interpretive properties that constrain the relation between them.
Jim Wood and Neil Myler
The topic “argument structure and morphology” refers to the interaction between the number and nature of the arguments taken by a given predicate on the one hand, and the morphological makeup of that predicate on the other. This domain turns out to be crucial to the study of a number of theoretical issues, including the nature of thematic representations, the proper treatment of irregularity (both morphophonological and morphosemantic), and the very place of morphology in the architecture of the grammar. A recurring question within all existing theoretical approaches is whether word formation should be conceived of as split across two “places” in the grammar, or as taking place in only one.
Gerrit Jan Dimmendaal
Nilo-Saharan, a phylum spread mainly across an area south of the Afro-Asiatic and north of the Niger-Congo phylum, was established as a genetic grouping by Greenberg. In his earlier, continent-wide classification of African languages in articles published between 1949 and 1954, Greenberg had proposed a Macro-Sudanic family (renamed Chari-Nile in subsequent studies), consisting of a Central Sudanic and an Eastern Sudanic branch plus two isolated members, Berta and Kunama. This family formed the core of the Nilo-Saharan phylum as postulated by Greenberg in his The Languages of Africa, where a number of groups were added which had been treated as isolated units in his earlier classificatory work: Songhay, Eastern Saharan (now called Saharan), Maban and Mimi, Nyangian (now called Kuliak or Rub), Temainian (Temeinian), Coman (Koman), and Gumuz.
Presenting an “encyclopaedic survey” of morphological structures for the more than 140 languages belonging to this phylum is impossible in such a brief study, also given the tremendous genetic distance between some of the major subgroups. Instead, typological variation in the morphological structure of these genetically-related languages will be central. In concrete terms this involves synchronic and diachronic observations on their formal properties (section 2), followed by an introduction to the nature of derivation, inflection, and compounding properties in Nilo-Saharan (section 3). This traditional compartmentalization has its limits because it misses out on the interaction with lexical structures and morphosyntactic properties in its extant members, as argued in section 4. As pointed out in section 5, language contact also must have played an important role in the geographical spreading of several of these typological properties.
Blending is a type of word formation in which two or more words are merged into one so that the blended constituents are either clipped, or partially overlap. An example of a typical blend is brunch, in which the beginning of the word breakfast is joined with the ending of the word lunch. In many cases such as motel (motor + hotel) or blizzaster (blizzard + disaster) the constituents of a blend overlap at segments that are phonologically or graphically identical. In some blends, both constituents retain their form as a result of overlap, for example, stoption (stop + option). These examples illustrate only a handful of the variety of forms blends may take; more exotic examples include formations like Thankshallowistmas (Thanksgiving + Halloween + Christmas). The visual and audial amalgamation in blends is reflected on the semantic level. It is common to form blends meaning a combination or a product of two objects or phenomena, such as an animal breed (e.g., zorse, a breed of zebra and horse), an interlanguage variety (e.g., franglais, which is a French blend of français and anglais meaning a mixture of French and English languages), or other type of mix (e.g., a shress is a type of clothes having features of both a shirt and a dress).
Blending as a word formation process can be regarded as a subtype of compounding because, like compounds, blends are formed of two (or sometimes more) content words and semantically either are hyponyms of one of their constituents, or exhibit some kind of paradigmatic relationships between the constituents. In contrast to compounds, however, the formation of blends is restricted by a number of phonological constraints given that the resulting formation is a single word. In particular, blends tend to be of the same length as the longest of their constituent words, and to preserve the main stress of one of their constituents. Certain regularities are also observed in terms of ordering of the words in a blend (e.g., shorter first, more frequent first), and in the position of the switch point, that is, where one blended word is cut off and switched to another (typically at the syllable boundary or at the onset/rime boundary). The regularities of blend formation can be related to the recognizability of the blended words.
Blocking can be defined as the non-occurrence of some linguistic form, whose existence could be expected on general grounds, due to the existence of a rival form. *Oxes, for example, is blocked by oxen, *stealer by thief. Although blocking is closely associated with morphology, in reality the competing “forms” can not only be morphemes or words, but can also be syntactic units. In German, for example, the compound Rotwein ‘red wine’ blocks the phrasal unit *roter Wein (in the relevant sense), just as the phrasal unit rote Rübe ‘beetroot; lit. red beet’ blocks the compound *Rotrübe. In these examples, one crucial factor determining blocking is synonymy; speakers apparently have a deep-rooted presumption against synonyms. Whether homonymy can also lead to a similar avoidance strategy, is still controversial. But even if homonymy blocking exists, it certainly is much less systematic than synonymy blocking.
In all the examples mentioned above, it is a word stored in the mental lexicon that blocks a rival formation. However, besides such cases of lexical blocking, one can observe blocking among productive patterns. Dutch has three suffixes for deriving agent nouns from verbal bases, -er, -der, and -aar. Of these three suffixes, the first one is the default choice, while -der and -aar are chosen in very specific phonological environments: as Geert Booij describes in The Morphology of Dutch (2002), “the suffix -aar occurs after stems ending in a coronal sonorant consonant preceded by schwa, and -der occurs after stems ending in /r/” (p. 122). Contrary to lexical blocking, the effect of this kind of pattern blocking does not depend on words stored in the mental lexicon and their token frequency but on abstract features (in the case at hand, phonological features).
Blocking was first recognized by the Indian grammarian Pāṇini in the 5th or 4th century
Bracketing paradoxes—constructions whose morphosyntactic and morpho-phonological structures appear to be irreconcilably at odds (e.g., unhappier)—are unanimously taken to point to truths about the derivational system that we have not yet grasped. Consider that the prefix un- must be structurally separate in some way from happier both for its own reasons (its [n] surprisingly does not assimilate in Place to a following consonant (e.g., u[n]popular)), and for reasons external to the prefix (the suffix -er must be insensitive to the presence of un-, as the comparative cannot attach to bases of three syllables or longer (e.g., *intelligenter)). But, un- must simultaneously be present in the derivation before -er is merged, so that unhappier can have the proper semantic reading (‘more unhappy’, and not ‘not happier’). Bracketing paradoxes emerged as a problem for generative accounts of both morphosyntax and morphophonology only in the 1970s. With the rise of restrictions on and technology used to describe and represent the behavior of affixes (e.g., the Affix-Ordering Generalization, Lexical Phonology and Morphology, the Prosodic Hierarchy), morphosyntacticians and phonologists were confronted with this type of inconsistent derivation in many unrelated languages.
Andrej L. Malchukov
Morphological case is conventionally defined as a system of marking of a dependent nominal for the type of relationship they bear to their heads. While most linguists would agree with this definition, in practice it is often a matter of controversy whether a certain marker X counts as case in language L, or how many case values language L features. First, the distinction between morphological cases and case particles/adpositions is fuzzy in a cross-linguistic perspective. Second, the distinctions between cases can be obscured by patterns of case syncretism, leading to different analyses of the underlying system. On the functional side, it is important to distinguish between syntactic (structural), semantic, and “pragmatic” cases, yet these distinctions are not clear-cut either, as syntactic cases historically arise from the two latter sources. Moreover, case paradigms of individual languages usually show a conflation between syntactic, semantic, and pragmatic cases (see the phenomenon of “focal ergativity,” where ergative case is used when the A argument is in focus). The composition of case paradigms can be shown to follow a certain typological pattern, which is captured by case hierarchy, as proposed by Greenberg and Blake, among others. Case hierarchy constrains the way how case systems evolve (or are reduced) across languages and derives from relative markedness and, ultimately, from frequencies of individual cases. The (one-dimensional) case hierarchy is, however, incapable of capturing all recurrent polysemies of individual case markers; rather, such polysemies can be represented through a more complex two-dimensional hierarchy (semantic map), which can also be given a diachronic interpretation.
Jessica Coon and Clint Parker
The phenomenon of case has been studied widely at both the descriptive and theoretical levels. Typological work on morphological case systems has provided a picture of the variability of case cross-linguistically. In particular, languages may differ with respect to whether or not arguments are marked with overt morphological case, the inventory of cases with which they may be marked, and the alignment of case marking (e.g., nominative-accusative vs. ergative-absolutive). In the theoretical realm, not only has morphological case been argued to play a role in multiple syntactic phenomena, but current generative work also debates the role of abstract case (i.e., Case) in the grammar: abstract case features have been proposed to underlie morphological case, and to license nominals in the derivation.
The phenomenon of case has been argued to play a role in at least three areas of the syntax reviewed here: (a) agreement, (b) A-movement, and (c) A’-movement. Morphological case has been shown to determine a nominal argument’s eligibility to participate in verbal agreement, and recent work has argued that languages vary as to whether movement to subject position is case-sensitive. As for case-sensitive A’-movement, recent literature on ergative extraction restrictions debates whether this phenomenon should be seen as another instance of “case discrimination” or whether the pattern arises from other properties of ergative languages. Finally, other works discussed here have examined agreement and A’-extraction patterns in languages with no visible case morphology. The presence of patterns and typological gaps—both in languages with overt morphological case and in those without it—lends support to the relevance of abstract case in the syntax.
The Causative/Inchoative alternation involves pairs of verbs, one of which is causative and the other non-causative syntactically and semantically (e.g., John broke the window vs. The window broke). In its causative use, an alternating verb is used transitively and understood as externally caused. When used non-causatively, the verb is intransitive and interpreted as spontaneous. The alternation typically exhibits an affected argument (i.e., a Theme) in both intransitive and transitive uses, whereas the transitive use also involves a Causer that brings about the event. Although they are often volitional agents (e.g., John broke the window with a stone), external causers may also be non-volitional causers (e.g., The earthquake broke the windows) and instruments (e.g., The hammer broke the window).
Morphologically, languages exhibit different patterns reflecting the alternation, even intralinguistically. In languages like English, alternations are not morphologically coded, but they are in most languages. Languages like Hindi commonly mark causative (or transitive) alternations by means of different mechanisms, such as internal vowel changes or causative morphology. In many European languages, a subset of alternating verbs may exhibit an uncoded alternation, but most alternating verbs mark anticausativization with a reflexive-like clitic. In Yaqui (Uto-Aztecan), different patterns are associated with different verbal roots. The alternation may be uncoded, equipollent (i.e., both alternating forms are coded), and anticausative.
Theoretically, different approaches have explored the alternation. Both lexical and syntactic causativization and anticausativization accounts have been proposed to explain the alternation. A third approach postulates that both forms are derived from a common source.
Pius ten Hacken
The scope of classical generative morphology is not clearly determined. All three components need clarification. The boundaries of what counts as generative linguistics are not unambiguously set, but it can be assumed that all generative work in linguistics is inspired by the work of Noam Chomsky. Morphology was a much more prominent component of linguistic theory in earlier approaches, but of course the subject field had to be accounted for also in generative linguistics. The label classical can be seen as restricting the scope both to the more mainstream approaches and to a period that ends before the present. Here, the early 1990s will be taken as the time when classical theorizing gave way to contemporary generative morphology.
In the earliest presentations of generative linguistics, there was no lexicon. The introduction of the lexicon made many of the ideas formulated before obsolete. Chomsky’s Lexicalist Hypothesis provided the basis for a new start of research in morphology. Two contrasting elaborations appeared in the early 1970s. Halle proposed a model based on the combination of morphemes, Jackendoff one based on the representation and analysis of full words.
Against this background, a number of characteristic issues were discussed in the 1970s and 1980s. One such issue was the form of rules. Here there was a shift from transformations to rewrite rules. This shift can be seen particularly well in the discussion of verbal compounds, e.g., truck driver. The question whether and how morphology should be distinguished from syntax generated a lot of discussion. Another broad question was the degree to which rules of morphology should be thought of as operating in separate components. This can be observed in the issue of the distinction of inflection and derivation and in level ordering. The latter was a proposal to divide affixes into classes with different phonological and other effects on the base they attach to. A side effect of level ordering was the appearance of bracketing paradoxes, where, for instance, generative grammarian has a phonological constituent grammarian but a semantic constituent generative grammar. Another aspect of rule application which can be constructed as a difference between morphology and syntax is productivity. In general, syntactic rules are more productive and morphological rules display blocking effects, where, for instance, unpossible is blocked by the existence of impossible.
Being classical, much of the discussions in this period serves as a shared background for the emergence and discussion of current generative approaches in morphology. The transition to these theories started in the 1990s, although some of them appeared only in the early 2000s.
Clinical linguistics is the branch of linguistics that applies linguistic concepts and theories to the study of language disorders. As the name suggests, clinical linguistics is a dual-facing discipline. Although the conceptual roots of this field are in linguistics, its domain of application is the vast array of clinical disorders that may compromise the use and understanding of language. Both dimensions of clinical linguistics can be addressed through an examination of specific linguistic deficits in individuals with neurodevelopmental disorders, craniofacial anomalies, adult-onset neurological impairments, psychiatric disorders, and neurodegenerative disorders. Clinical linguists are interested in the full range of linguistic deficits in these conditions, including phonetic deficits of children with cleft lip and palate, morphosyntactic errors in children with specific language impairment, and pragmatic language impairments in adults with schizophrenia.
Like many applied disciplines in linguistics, clinical linguistics sits at the intersection of a number of areas. The relationship of clinical linguistics to the study of communication disorders and to speech-language pathology (speech and language therapy in the United Kingdom) are two particularly important points of intersection. Speech-language pathology is the area of clinical practice that assesses and treats children and adults with communication disorders. All language disorders restrict an individual’s ability to communicate freely with others in a range of contexts and settings. So language disorders are first and foremost communication disorders. To understand language disorders, it is useful to think of them in terms of points of breakdown on a communication cycle that tracks the progress of a linguistic utterance from its conception in the mind of a speaker to its comprehension by a hearer. This cycle permits the introduction of a number of important distinctions in language pathology, such as the distinction between a receptive and an expressive language disorder, and between a developmental and an acquired language disorder. The cycle is also a useful model with which to conceptualize a range of communication disorders other than language disorders. These other disorders, which include hearing, voice, and fluency disorders, are also relevant to clinical linguistics.
Clinical linguistics draws on the conceptual resources of the full range of linguistic disciplines to describe and explain language disorders. These disciplines include phonetics, phonology, morphology, syntax, semantics, pragmatics, and discourse. Each of these linguistic disciplines contributes concepts and theories that can shed light on the nature of language disorder. A wide range of tools and approaches are used by clinical linguists and speech-language pathologists to assess, diagnose, and treat language disorders. They include the use of standardized and norm-referenced tests, communication checklists and profiles (some administered by clinicians, others by parents, teachers, and caregivers), and qualitative methods such as conversation analysis and discourse analysis. Finally, clinical linguists can contribute to debates about the nosology of language disorders. In order to do so, however, they must have an understanding of the place of language disorders in internationally recognized classification systems such as the 2013 Diagnostic and Statistical Manual of Mental Disorders (DSM-5) of the American Psychiatric Association.
Clitics can be defined as prosodically defective function words. They can belong to a number of syntactic categories, such as articles, pronouns, prepositions, complementizers, negative adverbs, or auxiliaries. They do not generally belong to open classes, like verbs, nouns, or adjectives. Their prosodically defective character is most often manifested by the absence of stress, which in turn correlates with vowel reduction in those languages that have it independently; sometimes the clitic can be just a consonant or a consonant cluster, with no vowel. This same prosodically defective character forces them to attach either to the word that follows them (proclisis) or to the word that precedes them (enclisis); in some cases they even appear inside a word (mesoclisis or endoclisis). The word to which a clitic attaches is called the host. In some languages (like some dialects of Italian or Catalan) enclitics can surface as stressed, but the presence of stress can be argued to be the result of assignment of stress to the host-clitic complex, not to the clitic itself. One consequence of clitics being prosodically defective is that they cannot be the sole element of an utterance, for instance as an answer to some question; they need to always appear with a host.
A useful distinction is that between simple clitics and special clitics. Simple clitics often have a nonclitic variant and appear in the expected syntactic position for nonclitics of their syntactic category. Much more attention has been paid in the literature to special clitics. Special clitics appear in a designated position within the clause or within the noun phrase (or determiner phrase). In several languages certain clitics must appear in second position, within the clause, as in most South Slavic languages, or within the noun phrase, as in Kwakw'ala. The pronominal clitics of Romance languages or Greek must have the verb as a host and appear in a position different from the full noun phrase. A much debated question is whether the position of special clitics is the result of syntactic movement, or whether other factors, morphological or phonological, intervene as well or are the sole motivation for their position. Clitics can also cluster, with some languages allowing only sequences of two clitics, and other languages allowing longer sequences. Here one relevant question is what determines the order of the clitics, with the main avenues of analysis being approaches based on syntactic movement, approaches based on the types of morphosyntactic features each clitic has, and approaches based on templates. An additional issue concerning clitic clusters is the incompatibility between specific clitics when combined and the changes that this incompatibility can provoke in the form of one or more of the clitics. Combinations of identical or nearly identical clitics are often disallowed, and the constraint known as the Person-Case Constraint (PCC) disallows combinations of clitics with a first or second person accusative clitic (a direct object, DO, clitic) and a third person (and sometimes also first or second person) dative clitic (an indirect object, IO, clitic). In all these cases either one of the clitics surfaces with the form of another clitic or one of the clitics does not surface; sometimes there is no possible output. Here again both syntactic and morphological approaches have been proposed.