Old Church Slavonic is an inflectional language with moderately complex verbal and nominal systems.
 The nominal case category distinguishes 7 cases for nouns, 6 for pronouns and adjectives (no vocative):
 Old Church Slavonic has three numbers: singular, dual, and plural.
 The dual, and not the plural, is used for nouns that are two. Nouns found in natural pairs, such as eyes, ears, and hands, are only found rarely in the plural. Due to its consistent use in all Old Church Slavonic texts, it appears to have been a living element of the language. The dual affects adjectives and verbs in addition to nouns.
 The nominative is used for the subject of a sentence, but it is only distinguished from the accusative in the masculine plural and the feminine singular, excluding the i-declension. Unlike in most modern Slavic languages, the nominative is also typically used for the complement of verbs meaning "to be". It is also used with verbs of naming and calling, but the accusative is also used for these verbs.
 The accusative case is used for the direct object of a sentence with transitive verbs. For the masculine o/jo declension, the accusative singular for "an adult, healthy, free male person" is often shown by the use of the endings of the genitive singular. The accusative is also used with nouns for a duration of time and a measure of distance. Old Church Slavonic makes more frequent use of the accusative case after negated infinitives and participles than other Slavic languages, and it is unclear if this is an innovation of Old Church Slavonic or an archaism.
 When used with nouns, the genitive frequently denotes the possessor of another noun or "the whole of which the other noun is a part", among other meanings. It is also used frequently with the numerals after five, and with certain pronouns, in the form of the partitive genitive.
 The genitive may be used as the complement of the 'verb to' to denote possession, and it replaces the nominative as the complement of 'to be' in impersonal sentences if the verb is negated. It is also used for the object of negated infinitives or participles, and for the objects of certain verbs. It is used after some adjectives, and for objects of comparison after adjectives in the comparative. When recording a date, the month is typically written in the genitive. Unlike other Slavic languages, there is no genitive of time.
 The dative case is used for the indirect object of a sentence. In addition, it is infrequently used to denote the goal of a motion (its original meaning), but this is more typically shown by using the preposition къ (kъ) followed by the dative. It is also used for the objects of verbs of commanding, obeying, favoring, giving, saying, showing, and promising, as well as for verbs meaning "to seem", and "to be similar to". Additionally, it can be used with nouns and adjectives, particularly in impersonal constructions. It can also be used for a "dative of advantage", showing for whom an action was performed, and as an "ethic dative" that shows "emphasis or emotional involvement". Moreover, the dative can also be used to show possession, typically showing a close relationship between the possessor and the thing possessed, in which form it can occur after the verb "to be" or adjoining the noun possessed. The dative is also used for the "dative absolute" construction, a type of subordinate clause, in which a participle, often with a noun subject, are both placed in the dative.
 The instrumental case can show the "instrument" by which an action was performed, mark "a part of the body or state of mind accompanying the action", and denote the manner in which something was performed. The instrumental can be used to denote measure following a comparison, how many times an action was performed with numerals, an instrumental of place showing over or through what a movement occurs, to denote the time of an action, to mean "in respect to" when use with verbs, adjectives, or other nouns, and to denote the cause of verb, among other meanings. It is also used to denote the agent in passive constructions.
 The instrumental is also found rarely for the complement of the verb "to be". It is not found in this meaning in the oldest Old Church Slavonic texts, the Gospels, and only occasionally in later texts.
 The locative case is used to denote the location in which something occurs. It very rarely occurs without a preceding preposition. Without a preposition, it is only used with place names, as a "locative of place". Due to more frequent use of locatives of place in Old Russian and Old Czech, it is possible that this rarity is caused by Old Church Slavonic following Greek syntax. It is also used, again rarely, for the "locative of time" to denote "in" a certain time. The locative is also used as the object of a small number of verbs; as this construction is extremely rare in other Slavic languages it is most likely an archaic form.
 The vocative is used instead of the nominative when a noun is used in isolation as an address or exclamation. Due to this case's consistent use in translations from Greek, in which the vocative is often identical to the nominative, it is clear that it was productive part of the spoken language.
 Nouns belonging to this declension class are generally masculines ending in -ъ in the nominative singular (богъ, градъ, родъ). The only exception are the nouns in -ъ that inflect as u-stem masculines.
 Sometimes (but not yet obligatorily, in contrast to later Slavic languages), in the accusative singular, the beginnings of a difference between an animate and inanimate subgender can be seen, as the genitive may occasionally be used instead of the accusative for animate objects (raba beside rabъ).
 
Nouns with the suffix анинъ/ꙗнинъ (-(j)an-in-ъ), for example гражданинъ, also belong to this declension class in the singular, but in the plural they lose the -in- interfix and conform to the consonantal paradigm (гражданє graždane, гражданъ graždanъ, гражданьмъ graždanьmъ, гражданꙑ graždany, гражданє graždane, гражданьхъ graždanьxъ, гражданꙑ graždany).
 
 Nouns belonging to this declension class are neuters ending in  -o in the nominative singular (сєло, лѣто, мѣсто). The only exception are the few neuters that are inflected as s-stems.
 
 Nouns belonging to this declension class are masculines ending in  -ь preceded by a palatal in the nominative singular (врачь, крал҄ь, кошь).
 This paradigm encompasses nouns such as краи (krai) that don't appear to be ending in a palatal, but are in fact underlyingly combinations like krajь and so undergo this declension (*край-ь kraj-ь, краꙗ kraj-a).
 Nouns ending in agentive suffixes -tel-ь and -ar-ь also belong to this class (ꙋчитєл҄ь: učitelь, učitelja, učitelju..., мꙑтарь: mytarь, mytarja, mytarju...).
  
 The jo-stem declension class encompasses neuters ending in  -e (ложє, полѥ, молєньє).
 
 Nouns belonging to this declension class are feminines ending in  -a preceded by a hard, non-palatal consonant (жєна).
 Also belonging to this paradigm are the rare masculines ending in -a (слꙋга, воѥвода).
 
 Noun belonging to this declension class are feminines ending in  -a preceded by a soft, palatal consonant (стража, свѣща, мрєжа).
 This paradigm also encompasses feminines ending in  -i (рабꙑн҄и, богꙑн҄и), -ica (дѣвица) and -ьni- (риꙁьница), and also masculines ending in  -a preceded by a palatal (юноша).
  
 Nouns belonging to this declension class are masculines ending in  -ь preceded by a hard, non-palatal consonant (чрьвь, господь, пѫть). The only exception are a limited number of such nouns belonging to the n-stem paradigm.
  
 Nouns belonging to the i-stem feminine declension are feminines ending in  -ь in the nominative singular (рѣчь, нощь, тварь).
 The only exception is the noun кръвь (krъvь) which undergoes ъv-stem (ū-stem) declension.
 
 Nouns belonging to this declension are a rather small group of masculines: чинъ, домъ, лєдъ, мєдъ, миръ, полъ, санъ, сꙑнъ, волъ, врьхъ.
 
 Nouns belonging to the ū-stem declension (also known as -ъv-' declension, or v-stem declension) are: бꙋкꙑ, брадꙑ, цѣлꙑ, црькꙑ, хорѫгꙑ, локꙑ, любꙑ, нєплодꙑ, рабꙑн҄и, прѣлюбꙑ, смокꙑ, свєкрꙑ, жрьнꙑ, крꙑ (this last form is attested in Psalterium Sinaiticum; older sources list the accusative form кръвь as a lemma).
 
 Nouns belonging to this declension class are the following masculines: дьнь, ѥлꙑ, ѩчьмꙑ, камꙑ, корꙑ, пламꙑ, рємꙑ, сѧжєнь, стєпєнь.
 
 Nouns belonging to this declension class are the following neuters: брѣмѧ, чисмѧ, имѧ, писмѧ, плємѧ, сѣмѧ, слѣмѧ, тѣмѧ, врѣмѧ.
 
 Nouns belonging to this declension class are the following neuters: чꙋдо, диво, дрѣво, коло, нєбо, тѣло, слово, as well as the dual forms of ꙋхо, око.
 
 The t-stem (also known as nt-stem) paradigm encompasses neuters denoting a young of an animal or human: отрочѧ, агнѧ, коꙁьлѧ, клюшѧ, осьлѧ, овьчѧ, тєлѧ, жрѣбѧ, etc.
 
 r-stem feminines are the nouns мати and дъщи.
 
 Just as the first and second person pronouns, the third person pronoun is commonly used only in oblique cases. Nominative singular forms are not attested in the OCS corpus, and are reconstructed. In the East South Slavic dialectal area where OCS originated, a suppletive nominative singular stem of the demonstrative tъ ('that') is used, elsewhere onъ ('that one there, yon'), or very rarely sь ('this').
 By attaching the enclitic particle že to the forms of *i one obtains the relative pronoun: iže ('he who'), ježe ('the (female) one to whom'), jejuže ('the two of whom'), etc.
 When following prepositions, these pronouns take a prothetic n-, hence kъ n'imъ ('to them') instead of *imъ, na n'emь ('on him'), etc. This is a remnant of final -m/n in the PIE prepositions *kom (cf. Latin cum, Sanskrit kám), 
 
The reflexive pronoun has only singular oblique forms, which is the state of affairs inherited from PIE *swé. The reflexive pronoun refers to the subject as a whole, and can be translated as English -self (myself, yourself, himself etc.)
 As mentioned, the third person pronoun *i participates in the formation of the relative pronoun by appending the indeclinable enclitic že. Unlike the third person pronoun, however, the nominative case forms do occur. Similarly, a prothetic n- occurs when following prepositions, e.g., vъ n'ьže ('in which').
 The interrogative pronoun ('who?, what?') has singular-only forms, with the masculine and feminine forms syncretized. Variant forms of čьto occurring in some of the oblique cases have been listed in parentheses.
 
 The interrogative adjective, sometimes also labelled as the interrogative pronoun ('which?, what sort of?'), also has some variant forms listed in parentheses.
 
 The possessive interrogative adjective, sometimes also labelled as the possessive interrogative pronoun ('whose?'), follows the same declension.
 
 The interrogative pronouns kъto, čьto can also have the indefinite meanings of 'anybody', 'anything' respectively.
 The prefix ně- imparts an indefinite meaning to the word to which it is attached: thus kъto ('who?') becomes někъto ('someone'), and čьto ('what?') becomes něčьto ('something'). Similarly, the prefix ni- imparts a negative meaning: nikъto ('no one'), ničьto ('nothing'). A prepositions may come between prefix and base word:
 OCS adjectives can be in two forms: short and long, corresponding to indefinite and definite meaning respectively. The long and short forms of the adjective have distinct syntactical roles. In general the long form is used attributively, whereas the short form is predicative: чловѣкъ добръ 'a good man, man is good'; чловѣкъ добръіи 'the good man, the man who is good'. The short form is indefinite in meaning, 'man is good'. The combination of a short-form adjective with substantive is used when the signified entity is presented as new, without prior reference. Hence въ пєшть огн҄ьнѫ 'into a furnace, a fiery one'. The long form, by contrast, acts as a pointer and is definite, 'the good man'. The long-form adjective with substantive combination is used when the adjective presents a quality known to be associated with the substantive modified. Hence въ гєонѫ огн҄ьнѫѭ 'into hell the fiery'. The compound form is often rendered in English by a relative clause: 'into the hell which is fiery'.  Adjectives used as substantives are themselves subject to the long and short form distinction. Again the long form refers to a substantive previously introduced or assumed known. Thus привѣшѧ къ н҄ємѹ слѣпа... и имъ слѣпаєго за рѫкѫ 'they brought to him a blind man... and having taken the blind man by the hand...'.  In a sequence of coordinated participles, when used as substantives, it is typical for only the first to use the long form. The following substantives use the short form. Hence слъішѧи словєса моја и творѧ ја... 'he who hears my words and does them...'.
 Indefinite adjectives are inflected as the corresponding nouns of the primary declension, e.g., novъ as rabъ, nova as žena, novo as selo, ništь as vračь, ništa as duša, nište as polje.
 Definite adjectives (also known as compound, long, or pronominal forms of adjective) are formed by suffixing to the indefinite form the anaphoric third-person pronoun jь (spelled as i in OCS orthography), ja, je as shown in the table.
 There are three levels of adjective gradation in OCS:
 The superlative is formed:
 The absolute superlative is formed:
 All ordinals are inflected like the corresponding adjectives.
 The present tense is formed by adding present-tense endings onto the present tense stem, which itself is sometimes hidden due to sound changes that have occurred in the past (more common verbs are listed):
 There are several classes of verbs:
 1. e-type verbs add the interfix -e- to the present stem (except in front of -ǫ) and the endings:
 2. i-type verbs exhibit the same set of endings, but this time the interfix is -i- (except in front of -ǫ and -ę). In the first person singular one finds the processes of iotation (k/c + j > č, g/z + j > ž, x/s + j > š, l + j > lj, n + j > nj, t + j > št, d + j > žd) and epenthesis (bj > blj, pj > plj, mj > mlj, vj > vlj):
 3. The athematic verbs byti, dati, věděti, iměti and jasti form the present tense irregularly:
 One should distinguish the verbs iměti (imamь, imaši, imatъ), imati (jemljǫ, jemleši, jemletъ) and jęti (imǫ, imeši, imetъ). Exceptional is also the verb xotěti which exhibits iotation even though it's not an i-type verb (xoštǫ, xošteši, xoštetъ).
 The aorist is used both to narrate individual events taking place at a specific time in the past, "without reference to other events taking place at the same time or subsequently" and to narrate the beginning or end of events of longer duration. Its most important function is to show that an event took place in the past, rather than to show that it is completed.
 The aorist form of imperfective verbs is used instead of the perfective aspect in the case of verbs of motion and perception, as well as of the verbs iměti, and jasti. Imperfective verbs in the aorist are also used when an entire action is negated, and may be used for verbs of saying, although the usual form for "he said" is from a perfective verb, reče.
 The asigmatic aorist (also called root or simple aorist) was named after the loss of the phoneme /s/ in the inflection (AGr. sigma), i.e. there is no VsV > VxV change (intervocalic /s/ yielding /x/). Over time, the asigmatic aorist became increasingly marked as an archaic language feature and was eventually replaced by the other two aorist formations.
 The asigmatic aorist was formed by adding to the infinitive stem of e-type verbs with stem ending in a consonant (i.e. verbs with the infix -nǫ-, which is dropped before the aorist endings, and verbs with the null infix) the following endings: -ъ, -e, -e; -omъ, -ete, -ǫ; -ově, -eta, -ete.
 2. pad -e
3. pad -e
 2. pad -ete
3. pad -ǫ
 2. pad -eta
3. pad -ete
 2. teč -e
3. teč -e
 2. teč -ete
3. tek -ǫ
 2. teč -eta
3. teč -ete
 2. mož -e
3. mož -e
 2. mož -ete
3. mog -ǫ
 2. mož -eta
3. mož -ete
 2. dviž -e
3. dviž -e
 2. dviž -ete
3. dvig -ǫ
 2. dviž -eta
3. dviž -ete
 The sigmatic or s-aorist was formed in the following ways:
 2. xvali
3. xvali
 2. xvali -s -te
3. xvali -š -ę
 2. xvali -s -ta
3. xvali -s -te
 2. teče
3. teče
 2. těste
3. těšę
 2. těsta
3. těste
 2. grebe
3. grebe
 2. grěste
3. grěsę
 2. grěsta
3. grěste
 2. bode
3. bode
 2. baste
3. basę
 2. basta
3. baste
 The new aorist (also known as ox-aorist) is formed by suffixing to the infinitive stem of e-type verbs ending in a consonant (verbs with the interfix -nǫ- and verbs with the null interfix) the interfix -os- (-ox) and onto it the endings -ъ, -, -; -omъ, -te, -ę; -ově, -ta, -te. Intervocalic sigma s changes into x.
 The 2nd and the 3rd person singular forms are not attested and thus the asigmatic aorist forms are taken as a replacement.
 2. (krad -e)
3. (krad -e)
 2. krad -os -te
3. krad -oš -ę
 2. krad -os -ta
3. krad -os -te
 2. (reč -e)
3. (reč -e)
 2. rek -os -te
3. rek -oš -ę
 2. rek -os -ta
3. rek -os -te
 2. (id -e)
3. (id -e)
 2. id -os -te
3. id -oš -ę
 2. id -os -ta
3. id -os -te
 The imperfect is used either for continuous or repeated actions in the past. It is typically used to form a background in a narration, and forms a contrast with the aorist and other verb forms: it often shows that an action took place at the same time as another. Actions in the imperfect are almost always incomplete, and the tense is typically only used with verbs in the imperfective aspect. Rarely, it can be formed with perfective verbs.
 There are two ways of forming the imperfect:
 1. If the infinitive stems ends in -a or -ě, the interfix -ax- is appended (which changes to -aš- according to the first palatalization in front of e) and onto it, the endings of the asigmatic aorist: -ъ, -e, -e; -omъ, -ete, -ǫ; -ově, -eta, -ete.
 2. glagola -aš -e
3. glagola -aš -e
 2. glagola -aš -ete
3. glagola -ax -ǫ
 2. glagola -aš -eta
3. glagola -aš -ete
 2. vidě -aš -e
3. vidě -aš -e
 2. vidě -aš -ete
3. vidě -ax -ǫ
 2. vidě -aš -eta
3. vidě -aš -ete
 2. The other way of forming the imperfect, applying to all other verbal stems, is by adding onto the present stem the interfix -ěax- (which, in accordance with the first palatalization, is changed to -ěaš- in front of e) and onto it the endings of asigmatic aorist: -ъ, -e, -e; -omъ, -ete, -ǫ; -ově, -eta, -ete.
 2. zov -ě -aš -e
3. zov -ě -aš -e
 2. zov -ě -aš -ete
3. zov -ě -ax -ǫ
 2. zov -ě -aš -eta
3. zov -ě -aš -ete
 2. bod -ě -aš -e
3. bod -ě -aš -e
 2. bod -ě -aš -ete
3. bod -ě -ax -ǫ
 2. bod -ě -aš -eta
3. bod -ě -aš -ete
 Both of these imperfect formations often occur side by side in verbs with stem alternation:
 In the texts of the OCS canon the forms are often contracted, so that ěax becomes ěx and aax becomes ax. An illustrating example is in Chernorizets Hrabar's famous work O pismenex "An Account of Letters":
 Some forms exhibit sound changes, namely palatalization or iotation in front of ě, yat thus turning into a. The same applies if the stem ends in j which is then reduced in front of yat and yat again changes into a:
 That the second form and not the first is the original one (the first being formed by the change of yat to a) is confirmed by the imperfect paradigm of the verb byti:
 2. běaše
3. běaše
 2. běašete
3. běaxǫ
 2. běašeta
3. běašete
 The present active participle is formed by adding the following endings to the present stem:
 1. e-type verbs and athematic verbs:
 2. e-type verbs whose present stem ends in a palatal:
 3. i-type verbs:
 The present passive participle is formed by suffixing to the present stem the endings -o/e/i + m + ъ/a/o (masculine, feminine, neuter):
 1. e-type verbs and athematic verbs:
 2. e-type verbs whose stem ends in a palatal:
 3. i-type verbs:
 The past active participle is formed by suffixing to the infinitive stem the following endings:
 1. e-type verbs and athematic verbs:
 2. i-type verbs exhibit epenthetic v, which eliminates hiatus:
 The latter i-type verbs have twofold forms of this participle – the mentioned one of older origin, and a newer one which arose due to analogical leveling:
 3. Verbs with liquid metathesis form this participle from its older stem form:
 4. Irregular participles:
 The l-participle (also known as the resultative participle or second past active participle) is formed by adding to the infinitive stem the interfix -l- and the endings ъ/a/o. If the stem ends in -t or -d, this consonant is dropped.
 The past passive participle is formed by suffixing to the infinitive stem the following endings:
 1. Verbs with stem ending in a consonant, -y or -i:
 2. Verbs with stem ending in -a or -ě:
 3. Verbs with stem ending in -ę, -u, -i and -ě (obtained by liquid metathesis):
 Of the latter verbs, those with stem ending in -i (viti, biti etc.) can also form the past passive participle like the verbs in the first group: bitъ or bijenъ, vitъ or vijenъ etc.).
 The perfect is formed by combining the l-participle with the imperfective present forms of the auxiliary verb byti.
 The pluperfect can be formed in multiple ways, by combining the l-participle with the perfect, imperfect or aorist formation of the auxiliary verb byti.
 The future tense is usually expressed using the present tense form of the perfective verb. Imperfective verbs form the future tense by combining the auxiliary verb (byti, xotěti, načęti, iměti) and the infinitive.
 The future perfect is formed by combining the l-participle with the perfective present of the auxiliary verb byti.
 The conditional (or conditional-optative) modal formation is formed by combining the l-participle with special modal forms of the auxiliary verb byti (with unattested dual forms):
 An alternative conditional is formed with the perfective aorist forms of byti:
 These are original adverbs with difficult to guess etymology and origin.
 Pronominal adverbs are derived by suffixing pronouns (e.g., ov + amo = ovamo, kъ + de = kъde):
 Nominal adverbs are derived from nominals or turn by conversion to adverbs which are in fact inflective lexemes with adverbial semantics.
 Modal adverbs are created with the suffixes -o or -ě (the endings of accusative and locative singular neuter gender respectively), with no difference in meanings between suffixes, although some adverbs have only the forms in -o (veselo), and some in -ě (javě).
 Modal adverbs could also be formed deadjectivally by means of the interfix -ьsk- and the ending -y (by origin, the instrumental plural ending; e.g., slověnьsky).
 Adverbs could also be formed with the suffix -ь (pravь, različь) and are by origin probably inherited Proto-Slavic accusative forms.
 Frequently occurring are the adverbialized a-stem instrumentals such as jednьnojǫ and also adverbially used oblique cases.
 Locative adverbs are by origin mostly petrified locative case forms of nouns: gorě, dolě, nizu, and the same can be said for temporal adverbs: zimě, polu dьne.
 The primary and non-derived prepositions are of PIE and PSl. heritage:
 The secondary prepositions are derived from adverbial expressions: vьslědъ from vь slědъ, prěžde is a comparative form of prědъ etc.
 Conjunctions and particles are not easily separable because they sometimes function as an intensifier, and sometimes as a conjunction.