In grammar, inflection or inflexion is the way language handles grammatical relations and relational categories such as tense, mood, voice, aspect, person, number, gender, case. In covert inflection, such categories are not overtly expressed. Overt inflection typically distinguishes lexical items (such as lexemes) from functional ones (such as affixes, clitics, particles and morphemes in general) and has functional items acting as markers on lexical ones. Lexical items that do not respond to overt inflection are typically invariant. Constraining cross-referencing inflection at the sentence level is known as concord or agreement.
In English many nouns are inflected for number with the inflectional plural affix -s (as in "dog" → "dog-s"), and most English verbs are inflected for tense with the inflectional past tense affix -ed (as in "call" → "call-ed").
English also inflects verbs by affixation to mark the third person singular in the present tense (with -s), and the present participle (with -ing). English short adjectives are inflected to mark comparative and superlative forms (with -er and -est respectively).
In the past, writers sometimes gave words such as doctor, Negro, dictator, professor, and orator Latin inflections to mark them as feminine, thus forming doctress, Negress, dictatrix, professress, and oratress. These inflected forms were never frequently used, although many English users continue to use Latin endings today in somewhat more common constructions such as actress, waitress, executrix, and dominatrix.
German, which is closely related to English, employs many of these inflectional devices, but the umlaut and ablaut are widespread, while in English they are generally considered as exceptions.
Two traditional grammatical terms refer to inflections of specific word classes:
Inflecting a nominal word is known as declining it, while inflecting a verb is called conjugating it. An organized list of the inflected forms of a given lexeme is also called its inflection, declension, or conjugation, as the case may be.
Below is an example of the declension of the English pronoun I, which is inflected for case and number.
The pronoun who is also inflected in conservative English, though only according to case. One can say that its declension is defective, in the sense that it lacks a reflexive form.
|singular & plural|
|tense||I||you||he, she, it||we||you||they|
The non-finite forms arrive (bare infinitive), arrived (past participle) and arriving (gerund/present participle), although not inflected for person or number, can also be regarded as part of the conjugation of the verb to arrive. Compound verb forms like I have arrived, I had arrived, or I will arrive can be included also in the conjugation of this verb for didactical purposes, but are not conjugations of arrive in the strictest morphological sense. Rather, they should be analysed as complex verb phrases with the structure
pronoun + conjugated auxiliary verb + non-finite form of main verb.
A class of words with similar inflection rules is called an inflectional paradigm. Nominal inflectional paradigms are also called declensions, and verbal inflectional paradigms are called conjugations. For example, in Old English nouns could be divided into two major declensions, the strong and the weak, inflected as is shown below:
|gender and number|
|case||Strong Noun Declension|
|engel 'angel'||scip 'ship'||sorg 'sorrow'|
|case||Weak Noun Declension|
|nama 'name'||ēage 'eye'||tunge 'tongue'|
These two terms, however, seem to be biased toward well-known dependent-marking languages (such as the Indo-European languages, or Japanese). In dependent-marking languages, nouns in adpositional phrases can carry inflectional morphemes. (Adpositions include prepositions and postpositions.) In head-marking languages, the adpositions can carry the inflection in adpositional phrases. This means that these languages will have inflected adpositions. In Western Apache (San Carlos dialect), the postposition -ká’ 'on' is inflected for person and number with prefixes.
|COLSPAN=2 align="center"||Singular||COLSPAN=2 align="center"||Dual||COLSPAN=2 align="center"||Plural|
|1st||shi-ká’||'on me'||noh-ká’||'on us two'||da-noh-ká’||'on us'|
|2nd||ni-ká’||'on you'||nohwi-ká’||'on you two'||da-nohwi-ká’||'on you all'|
|3rd||bi-ká’||'on him'||COLSPAN=2 align="center"||-||da-bi-ká’||'on them'|
Traditional grammars have specific terms for inflections of nouns and verbs, but not for those of adpositions.
See main article: Derivation (linguistics).
Inflection is the process of adding inflectional morphemes (atomic meaning units) to a word, which may indicate grammatical information (for example, case, number, person, gender or word class, mood, tense, or aspect). Compare with derivational morphemes, which create a new word from an existing word, sometimes by simply changing grammatical category (for example, changing a noun to a verb).
Words generally do not appear in dictionaries with inflectional morphemes. But they often do appear with derivational morphemes. For instance, English dictionaries list readable and readability, words with derivational suffixes, along with their root read. However, no traditional English dictionary will list book as one entry and books as a separate entry nor will they list jump and jumped as two different entries.
In some languages, inflected words do not appear in a fundamental form (the root morpheme) except in dictionaries and grammars.
See main article: Inflectional morphology.
Languages that add inflectional morphemes to words are sometimes called inflectional languages. Morphemes may be added in several different ways:
Affixing includes prefixing (adding before the base), and suffixing (adding after the base), as well as the much less common infixing (inside) and circumfixing (a combination of prefix and suffix).
See main article: morphological typology.
Inflection is sometimes confused with synthesis in languages. The two terms are related but not the same. Languages are broadly classified morphologically into analytic and synthetic categories, or more realistically along a continuum between the two extremes. Analytic languages isolate meaning into individual words, whereas synthetic languages create words not found in the dictionary by fusing or agglutinating morphemes, sometimes to the extent of having a whole sentence's worth of meaning in a single word. Inflected languages by definition fall into the synthetic category, though not all synthetic languages need be inflected.
All Indo-European languages, such as Albanian, English, German, Russian, Persian (Fârsi), Italian, Spanish, French, Sanskrit, and Hindi are inflected to a greater or lesser extent. In general, older Indo-European languages such as Latin, Irish, Slavic, Latvian, Lithuanian, and more prominently Greek and Sanskrit in all their historical forms, are extensively inflected. Deflexion caused newer languages such as English and French to lose much of their historical inflection. Afrikaans, an extremely young language, is almost completely uninflected and borders on being analytic. Some branches of Indo-European (for example, the Slavic languages, the Celtic languages, and the Romance languages) have generally retained more inflection than others (such as many Germanic languages, with the notable exception of Icelandic).
Old English was a moderately inflected language, using an extensive case system similar to that of modern Icelandic or German. Middle and Modern English lost progressively more of the Old English inflectional system. Modern English is considered a weakly inflected language, since its nouns have only vestiges of inflection (plurals, the pronouns), and its regular verbs have only four forms: an inflected form for the past indicative and subjunctive (looked), an inflected form for the third-person-singular present indicative (looks), an inflected form for the present participle (looking), and an uninflected form for everything else (look). While the English possessive indicator 's (as in "Jane's book") is a remnant of the Old English genitive case suffix, it is now not a suffix but a clitic. See also Declension in English.
Old Norse was inflected, but modern Swedish, Norwegian and Danish have, like English, lost almost all inflection. Icelandic preserves almost all of the inflections of Old Norse and has added its own. Modern German remains moderately inflected, retaining four noun cases, although the genitive had already began falling into disuse in all but formal writing in Early New High German, inspiring the title of the 2004 bestseller Der Dativ ist dem Genitiv sein Tod ("the dative is the death of the genitive", using the dative where archaic or formal writing would use the genitive). The case system of Dutch, simpler than German's, is also becoming more simplified in common usage. Afrikaans, recognized as a distinct language in its own right rather than a Dutch dialect only in the early 20th century, has lost almost all inflection.
The Romance languages, such as Spanish, Italian, French, Portuguese and Romanian, have more inflection than English, especially in verb conjugation. A single morpheme usually carries information about person, number, tense, aspect and mood, and the verb paradigm may be quite complex. Adjectives, nouns and articles are considerably less inflected, but they still have different forms according to number and grammatical gender.
Latin was even more inflected; nouns and adjectives had different forms according to their grammatical case (with several patterns of declension, and three genders instead of the two found in most Romance tongues), and there were synthetic perfective and passive voice verb forms.
The Baltic languages (presented nowadays by Lithuanian and Latvian) are moderately inflected retaining a number of archaic Indo-European features in their grammar. Nouns and adjectives are declined in seven cases. Some grammars define more cases based on two priciples:
Modern Baltic languages have also retained the old dual number. However, it is nowadays considered obsolete and included in grammar books as a reference and not as compulsory learning material. For instance, in standard Lithuanian it is normal to say "dvi varnos (pl.) - two crows" instead of "dvi varni (du.)".
Adjectives, pronouns, and numerals are declined for number, gender, and case to agree with the noun they modify/substitute. With a set of special pronominal forms, as well as four degrees of comparison, Lithuanian adjectives, for example, have the total of 147 synthetic forms.
Baltic verbs are inflected for tense, mood, aspect, and voice. They also agree with the subject in person and number (not in all forms in modern Latvian). They also demonstrate moderate fusion and high irregularity with the old morpheme seams dimmed by further evolution.
The Slavic languages, including Russian, Polish, Macedonian, Czech, Slovak, Croatian, Bosnian, Serbian, Ukrainian, Bulgarian, and Slovenian among others, all make use of a high degree of inflection, typically having six or seven cases and three genders (however, the case system has disappeared almost completely in modern Bulgarian and Macedonian, except for the vocative).
Declensional endings depend on case (nominative, genitive, dative, accusative, locative, instrumental, vocative), number (singular, dual or plural), gender (masculine, feminine, neuter) and animacy (animate vs inanimate). Unusual in other language families, declension in most Slavic languages also depends on whether the word is a noun or an adjective. Slovenian and Sorbian languages use a rare third number, (in addition to singular and plural numbers) known as dual. In addition, in some Slavic languages, such as Polish, word stems are frequently modified by the addition or absence of endings, resulting in consonant and vowel alternation.
Arabic (Arabic: اللغة العربية الفصحى, "Al-Luġah al-‘Arabiyyah al-Fuṣḥā"), or more precisely "Modern Standard Arabic (also called "Literary Arabic"), is a highly-inflected language. It uses a complex system of pronouns and their respective prefixes and suffixes for verb, noun, adjective and possessive conjugation. In addition, the system known as al-‘Irāb places vowel suffixes on each verb, noun, adjective, and adverb, according to its function within a sentence and its relation to surrounding words.
The following table () is an example of present-tense case applications in Arabic:
|Pronoun||Possessive Suffix||Verb Affixes||Pronoun||Possess. Suffix||Verb Affixes||Pronoun||Possess. Suffix||Verb Affixes|
|I||Arabic: أنا <small>''/anā/''</small>||Arabic: ــي <small>''/—ī/''</small>||Arabic: أ <small>''/a—/''</small>||Arabic: نحن <small>''/naḥnu/''</small>||Arabic: ــنا <small>''/—nā/''</small>||Arabic: نــ <small>''/n—/''</small>||-||-||-|
|you (masc.)||Arabic: أنتَ <small>''/anta/''</small>||Arabic: ــكَ <small>''/—ka/''</small>||Arabic: تــــــ <small>''/t—/</small>''||Arabic: أنتم <small>''/antum/</small>''||Arabic: ــكم <small>''/—kum/</small>''||Arabic: تــــــــــــون <small>''/t—ūn/</small>''||Arabic: أنتما <small>''/antumā/</small>''||Arabic: ــكما <small>''/—kumā/</small>''||Arabic: تــــــــــــان <small>''/t—ān/</small>''|
|you (fem.)||Arabic: أنتِ <small>''/anti/</small>''||Arabic: ــكِ <small>''/—ka/</small>''||Arabic: تــــــــــــين <small>''/t—īna/</small>''||Arabic: أنتنّ <small>''/antunna/</small>''||Arabic: ــكنّ <small>''/—kunna/</small>''||Arabic: تــــــــــــنّ <small>''/t—nna/</small>''||"||"||"|
|he||Arabic: هو <small>''/huwa/</small>''||Arabic: ــه <small>''/—hu/</small>''||Arabic: يــ <small>''/y—/</small>''||Arabic: هم <small>''/hum/</small>''||Arabic: ــهم <small>''/—hum/</small>''||Arabic: يـــــــــــــون <small>''/y—ūn/</small>''||Arabic: هما <small>''/humā/</small>''||Arabic: ــهما <small>''/—humā/</small>''||Arabic: يــــــــــــان <small>''/y—ān/</small>''|
|she||Arabic: هي <small>''/hiya/</small>''||Arabic: ــها <small>''/—ha/</small>''||Arabic: تــ <small>''/t—/</small>''||Arabic: هنّ <small>''/hunna/</small>''||Arabic: ــهنّ <small>''/—hunna/</small>''||Arabic: تــــــــــــنّ <small>''/t—nna/</small>''||"||"||"|
Arabic regional dialects (e.g. Moroccan Arabic, Egyptian Arabic, Gulf Arabic), used for everyday communication, tend to have less inflection than the more formal Literary Arabic. For example, in Jordanian Arabic, the second- and third-person feminine plurals (Arabic: أنتنّ /antunna/ and Arabic: هنّ /hunna/) and their respective unique conjugations are lost and replaced by the masculine (Arabic: أنتم /antum/ and Arabic: هم /hum/).
The Uralic languages (comprising Finno-Ugric and Samoyedic) are agglutinative, following from the agglutination in Proto-Uralic. The largest languages are Hungarian, Finnish and Estonian, all European Union official languages. Uralic inflection is, or is developed from, affixing. Grammatical markers directly added to the word perform the same function as prepositions in English. Almost all words are inflected according to their roles in the sentence: verbs, nouns, pronouns, numerals, adjectives, and some particles.
Hungarian and Finnish, in particular, often simply concatenate suffixes. For example, Finnish talossanikinko "in my house, too?" consists of talo-ssa-ni-kin-ko. However, in the Finnic languages (Finnish, Estonian, Sami), there are processes which affect the root, particularly consonant gradation. The original suffixes may disappear (and appear only by liaison), leaving behind the modification of the root. This process is extensively developed in Estonian and Sami, and makes them also inflected, not only agglutinating languages. The Estonian accusative case, for example, is expressed by a modified root: maja →majja (historical form *majam).
Basque, a language isolate, is an extremely inflected language, heavily inflecting both nouns and verbs. A Basque noun is inflected in 17 different ways for case, multiplied by 4 ways for its definiteness and number. These first 68 forms are further modified based on other parts of the sentence, which in turn are inflected for the noun again. It is estimated that at two levels of recursion, a Basque noun may have 458,683 inflected forms. Verb forms are similarly complex, agreeing with the subject, the direct object and several other arguments.
Some of the major Eastern Asian languages (such as the various Chinese languages, Vietnamese, and Thai) are not overtly inflected, or show very little overt inflection (though they used to show more), so they are considered analytic languages (also known as isolating languages).
Japanese shows a high degree of overt inflection on verbs, less so on adjectives, and very little on nouns, but it is always strictly agglutinative and extremely regular. Formally, every noun phrase must be marked for case, but this is done by invariable particles (clitic postpositions). (Many grammarians consider Japanese particles to be separate words, and therefore not an inflection, while others consider agglutination a type of overt inflection, and therefore consider Japanese nouns as overtly inflected.)
The Chinese family of languages, in general, does not possess overt inflectional morphology. Chinese words generally comprise of one or two syllables, each of which corresponds to a written character and individual morpheme. Since most morphemes are monosyllabic in the Chinese languages, Chinese is quite resistant to inflectional changes; instead, Chinese uses lexical means for achieving covert inflectional transparency. While European languages more often use overt inflection to mark a word's function in a sentence, the Chinese languages tend to use word order as a grammatical marking system. Whereas in English the first-person singular nominative "I" changes to "me" when used in the accusative - that is, when "I" is the object of a verb - Chinese simply uses word order to mark such a distinction. An example from Mandarin: 我给了他一本书 (wǒ gěile tā yī běn shū) 'I gave him a book'. Here 我 (wǒ) means 'I' and 他 (tā) means 'him'. However, 'He gave me a book' would be: 他给了我一本书 (tā gěile wǒ yī běn shū). 我 (Wǒ) and 他 (Tā) simply change places in the sentence to indicate that their case has switched: there is no overt inflection in the form of the words. In classical Chinese, pronouns were overtly inflected as to case. However, these overt case forms are no longer used; most of the alternative pronouns are considered archaic in modern Mandarin Chinese. Classically, 我 (wǒ) was used solely as the first person accusative. 吾 (Wú) was generally used as the first person nominative. 
Auxiliary languages, such as Esperanto, Ido, and Interlingua have comparatively simple inflectional systems.
In Esperanto, nouns and adjectives are inflected for case (nominative, accusative) and number (singular, plural), according to a simple paradigm without irregularities. Verbs are not inflected for person or number, but they are inflected for tense (past, present, future) and mood (indicative, infinitive, conditional, jussive). They also form active and passive participles, which may be past, present or future. All verbs are regular. (See main article on Esperanto grammar.)
Ido has a different form for each verbal tense (past, present, future, volitive and imperative) plus an infinitive, and both a present and past participle. There are though no inflections for person or number and all verbs are regular.
Nouns are marked for number (singular and plural), and the accusative case may be shown in certain situations, typically when the direct object of a sentence precedes its verb. On the other hand, adjectives are unmarked for gender, number or case (unless they stand on their own, without a noun, in which case they take on the same desinences as the missing noun would have taken). The definite article "la" ("the") remains unaltered regardless of gender or case, and also of number, except when there is no other word to show plurality. Pronouns are identical in all cases, though exceptionally the accusative case may be marked, as for nouns.
Interlingua, in contrast with the Romance languages, has no irregular verb conjugations, and its verb forms are the same for all persons and numbers. It does, however, have compound verb tenses similar to those in the Romance, Germanic, and Slavic languages: ille ha vivite, "he has lived"; illa habeva vivite, "she had lived". Nouns are inflected by number, taking a plural -s, but rarely by gender: only when referring to a male or female being. Interlingua has no noun-adjective agreement by gender, number, or case. As a result, adjectives ordinarily have no inflections. They may take the plural form if they are being used in place of a noun: le povres, "the poor".