Latin is a heavily inflected language with largely free word order. Nouns are inflected for number and case; pronouns and adjectives (including participles) are inflected for number, case, and gender; and verbs are inflected for person, number, tense, aspect, voice, and mood. The inflections are often changes in the ending of a word, but can be more complicated, especially with verbs.

Thus verbs can take any of over 100 different endings to express different meanings, for example regō "I rule", regor "I am ruled", regere "to rule", regī "to be ruled". Most verbal forms consist of a single word, but some tenses are formed from part of the verb sum "I am" added to a participle; for example, ductus sum "I was led" or ductūrus est "he is going to lead".

Classified things (represented by common nouns) belong to one of three grammatical genders (masculine, feminine, and neuter). The gender of the classified thing is realized by the last syllables of the adjectives, numbers and pronouns that refer to it: e.g. male animals such as hic vir "this man" and hic gallus "this cock", female animals such as haec mulier "this woman" and haec gallīna "this chicken", and either sexually undifferentiated animals such as hoc ovum "this egg" or stuff in general such as hoc "this thing". Specific kinds of stuff and abstract things also have one of the three grammatical genders. There are also two numbers: singular (mulier "woman") and plural (mulierēs "women").

As well as having gender and number, nouns, adjectives, and pronouns have different endings according to their function in the sentence, for example, rēx "the king" (subject), but rēgem "the king" (object). These different endings are called "cases". Most nouns have five cases: nominative (subject), accusative (object), genitive ("of"), dative ("to" or "for"), and ablative ("with" or "in"). Nouns for people (potential addressees) have the vocative (used for addressing someone). Nouns for places have a seventh case, the locative; this is mostly found with the names of towns and cities, e.g. Rōmae "in Rome".

There is no definite or indefinite article in Latin, so that rēx can mean "king", "a king", or "the king" according to context.

Latin word order tends to be subject–object–verb; however, other word orders are common. Different word orders are used to express different shades of emphasis. (See Latin word order.)

An adjective can come either before or after a noun, e.g. vir bonus or bonus vir "a good man", although some kinds of adjectives, such as adjectives of nationality (vir Rōmānus "a Roman man") usually follow the noun.

Latin is a pro-drop language; that is, pronouns in the subject are usually omitted except for emphasis, so for example amās by itself means "you love" without the need to add the pronoun tū "you". Latin also exhibits verb framing in which the path of motion is encoded into the verb rather than shown by a separate word or phrase. For example, the Latin verb exit (a compound of ex and it) means "he/she/it goes out".

In this article a line over a vowel (e.g. ē) indicates that it is long.

Pronouns are of two kinds, personal pronouns and 3rd person pronouns. Personal pronouns decline as follows.

mē, tē, nōs, vōs can also be used reflexively ("I see myself" etc.).^[28]

Nōs is frequently used in classical Latin for "I", but vōs is never used in a singular sense.^[29]

The genitive nostrum is used partitively (ūnusquisque nostrum "each one of us"), nostrī objectively (memor nostrī "remembering us, mindful of us").^[30][28]

3rd person pronouns are those such as hic "this" and ipse "(he) himself". The 3rd person pronouns can also be used adjectivally (except that quid "what?" when adjectival becomes quod). The declension of these pronouns tends to be irregular. They generally have -īus in the genitive singular, and -ī in the dative singular. In a few pronouns (illud "that", istud "that (of yours)", id "it, that", quod "which", quid "anything; what?", aliud "another", aliquid "something") the neuter singular ends in -d.

The declension of ille "that" is as follows:^[31]

Ipse "he himself" is very similar, except that the neuter singular ipsum ends in -m instead of -d.

Other very common 3rd person pronouns are hic, haec, hoc "this" and is, ea, id "he, she, it; that". Like other 3rd person pronouns, these can be used either independently (is "he") or adjectivally (is homō "that man"):

Before a vowel, hic and hoc are pronounced as if spelled hicc and hocc. Huius is pronounced as if spelled huiius with a long first syllable.^[32]

Also very common is the relative pronoun quī, quae, quod "who, which". The interrogative quis? quid? "who? what?" and indefinite quis, qua, quid "anyone, anything" are similar apart from the nominative singular:^[33]

Like adjectives, pronouns must agree in gender, case, and number with the nouns they refer to, as in the following, where hic is masculine agreeing with amor, but haec is feminine, agreeing with patria:

hic amor, haec patria est = this is my love, this my country^[34]

There is no indefinite article or definite article (the, a, an). Sometimes the weak determiner is, ea, id (English "that, this") can serve for the definite article:

Persuāsīt populō ut eā pecūniā classis aedificārētur^[35]

"He persuaded the people that a fleet should be built with the money (with that money)"

Adverbs modify verbs, adjectives and other adverbs by indicating time, place or manner. Latin adverbs are indeclinable and invariable. Like adjectives, adverbs have positive, comparative and superlative forms.

The positive form of an adverb can often be formed from an adjective by appending the suffix -ē (2nd declension adjectives) or -(t)er (3rd declension adjectives). Thus the adjective clārus, -a, -um, which means "bright", can be contrasted to the adverb clārē, which means "brightly". The adverbial ending -(i)ter is used to form adverbs from 3rd declension adjectives, for example celer "quick", celeriter "quickly". Other endings such as -ō, -e, -tim are also found.

The comparative form of an adverb is the same as the neuter nominative singular form of a comparative adjective and usually ends in -ius. Instead of the adjective clārior, which means "brighter", the adverb is clārius, which means "more brightly".

The superlative adverb has the same base as the superlative adjective and always ends in a long -ē. Instead of the adjective clārissimus, which mean "very bright" or "brightest", the adverb is clārissimē, which means "very brightly" or "most brightly".

The first three numbers have masculine, feminine and neuter forms fully declined as follows:^[42]

ūnus (one) can also be used in the plural, with plural-only nouns, e.g. ūna castra "one camp", ūnae litterae "one letter". For larger numbers plural-only nouns use special numerals: bīna castra "two camps", trīna castra "three camps". (See Latin numerals.)

The numbers quattuor (four) through decem (ten) are not declined:

quattuor (4)

quīnque (5)

sex (6)

septem (7)

octō (8)

novem (9)

decem (10)

The "tens" numbers are also not declined:

vīgintī (20)

trīgintā (30)

quadrāgintā (40)

quīnquāgintā (50)

sexāgintā (60)

septuāgintā (70)

octōgintā (80)

nōnāgintā (90)

The numbers 11 to 17 are formed by affixation of the corresponding digit to the base -decim, hence ūndecim, duodecim, tredecim, quattuordecim, quīndecim, sēdecim, septendecim. The numbers 18 and 19 are formed by subtracting 2 and 1, respectively, from 20: duodēvīgintī and ūndēvīgintī. For the numbers 21 to 27, the digits either follow or are added to 20 by the conjunction et: vīgintī ūnus or ūnus et vīgintī, vīgintī duo or duo et vīgintī etc. The numbers 28 and 29 are again formed by subtraction: duodētrīgintā and ūndētrīgintā. Each group of ten numerals through 100 follows the patterns of the 20s but 98 is nōnāgintā octō and 99 is nōnāgintā novem rather than *duodēcentum and *ūndēcentum respectively.

Compounds ending in 1 2 and 3 are the only ones to decline:

I saw 20 blackbirds = vīgintī merulās vīdī

I saw 22 blackbirds = vīgintī duās merulās vīdī (where duās changes to agree with merulās)

The "hundreds" numbers are the following:

centum (indeclinable)

ducentī, -ae, -a (200)

trecentī, -ae, -a (300)

quadringentī, -ae, -a (400)

quīngentī, -ae, -a (500)

sēscentī, -ae, -a (600)

septingentī, -ae, -a (700)

octingentī, -ae, -a (800)

nōngentī, -ae, -a (900)

However, 1000 is mille, an indeclinable adjective, but multiples such as duo mīlia (2000) have mīlia as a neuter plural substantive followed by a partitive genitive:

I saw a thousand lions = mīlle leōnēs vīdī

I saw three thousand lions = tria mīlia leōnum vīdī

Ordinal numbers are all adjectives with regular first- and second-declension endings. Most are built off of the stems of cardinal numbers (for example, trīcēsimus, -a, -um (30th) from trīgintā (30), sēscentēsimus, -a, -um nōnus, -a, -um (609th) for sēscentī novem (609). However, "first" is prīmus, -a, -um, and "second" is secundus, -a, -um (literally "following" the first; sequi means "to follow").

Latin allows a very flexible word order because of its inflectional syntax. Ordinary prose tended to follow the pattern of subject, direct object, indirect object, adverbial words or phrases, verb (with the proviso that when noun and verb make a compound, as impetum facio "I attack / make an attack" the noun is generally placed close to the verb).^[48] Any extra but subordinate verb, such as an infinitive, is placed before the main verb. Adjectives and participles usually directly follow nouns unless they are adjectives of beauty, size, quantity, goodness, or truth, in which case they usually precede the noun being modified. However, departures from these rules are frequent.

Relative clauses are commonly placed after the antecedent that the relative pronoun describes. Since grammatical function in a sentence is based not on word order but on inflection, the usual word order in Latin was often abandoned with no detriment to understanding but with various changes in emphasis.

While these patterns of word order were the most frequent in Classical Latin prose, they were frequently varied. The strongest surviving evidence suggests that the word order of colloquial Latin was mostly Subject-Object-Verb. That can be found in some very conservative Romance languages, such as Sardinian and Sicilian in which the verb is still often placed at the end of the sentence (see Vulgar Latin). On the other hand, subject-verb-object word order was probably also common in ancient Latin conversation, as it is prominent in the Romance languages, which evolved from Latin.^[49]

In poetry, however, word order was often changed for the sake of the meter for which vowel quantity (short vowels vs. long vowels and diphthongs) and consonant clusters, not rhyme and word stress, governed the patterns. One must bear in mind that poets in the Roman world wrote primarily for the ear, not the eye; many premiered their work in recitation for an audience. Hence, variations in word order served a rhetorical as well as a metrical purpose; they certainly did not prevent understanding.

In Virgil's Eclogues, for example, he writes, Omnia vincit amor, et nōs cēdāmus amōrī!: "Love conquers all, let us too yield to love!". The words omnia (all), amor (love) and amōrī (to love) are thrown into relief by their unusual position in their respective phrases.

The ending of the common Roman name Mārcus is different in each of the following pairs of examples because of its grammatical usage in each pair. The ordering in the second sentence of each pair would be correct in Latin and clearly understood, whereas in English it is awkward, at best, and meaningless, at worst:

Mārcus ferit Cornēliam: Marcus hits Cornelia. (subject–verb–object)

Mārcus Cornēliam ferit: Marcus Cornelia hits. (subject–object–verb)

Cornēlia dedit Mārcō dōnum: Cornelia gave Marcus a gift. (subject–verb–indirect object–direct object)

Cornēlia Mārcō dōnum dedit: Cornelia (to) Marcus a gift gave. (subject–indirect object–direct object–verb)

• Declension of Greek nouns in Latin
• Latin syntax
• Latin mnemonics
• Latin word order
• Latin numerals

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