Old Armenian had preserved to some degree the general morphological character of older Indo-European languages based on the inflexion of nouns and verbs. It was close typologically to Greek, though the shapes of words were very, even surprisingly, different. The nominal and pronominal declension had seven cases: nominative, genitive, dative, accusative, ablative, instrumental, and locative. However, many of these forms overlapped so that usually only three or four different forms existed; e.g., žam ‘time’ was both nominative and accusative, žamê was ablative, and žamu was genitive, dative, instrumental, and locative. A special form of locative was very rare. There was no gender category. The case endings varied for various types of stems.

By means of distinctive endings, the verb distinguished three persons in singular and plural. The tenses were based on the present stem (present, imperfect, subjunctive present, and prohibitive) and the aorist past stem (aorist, subjunctive aorist, and imperative).

The Modern Armenian noun has maintained and even developed this plan, especially in Eastern Armenian, which has the special locative ending -um in its declension. But, in comparison with Old Armenian (where case endings were different in singular and plural), Modern Armenian declension resembles rather the Turkish or the Georgian type of agglutination. This resemblance is especially visible in Eastern Armenian, where plural forms usually have the same endings as the singular—for example, -i for genitive and dative, the only difference residing in the plural infixation -ner- inserted between the stem and the ending for multisyllabic nouns—e.g., ašakert ‘pupil,’ ašakert-i ‘of pupil, to pupil,’ ašakert-ner-i ‘of pupils, to pupils.’

There are significant differences between Eastern and Western Armenian in case endings and in the use of the definite article, expressed as -ə (after consonants) and -n (after vowels). For instance, in Eastern Armenian the definite article may not be used after the genitive: pat(-ə) ‘(the) wall,’ pat-i ‘of (the) wall,’ pat-er(-ə) ‘(the) walls,’ pat-er-i both ‘of walls’ and ‘of the walls.’ In contrast, Western Armenian usage is, respectively, bad(-ə) ‘(the) wall,’ bad-i ‘of wall,’ bad-i-n ‘of the wall,’ bad-er(-ə) ‘(the) walls,’ bad-er-u ‘of walls,’ and bad-er-u-n ‘of the walls.’ Western Armenian has retained the Old Armenian ablative ending -ê, whereas Eastern Armenian has -ic‘; for instance, ‘from Armenia’ is rendered as Hayastan-ê-n (with -n being the definite article) in Western Armenian and as Hayastan-ic‘ in Eastern Armenian.

There are essential differences in the verb structures of the two varieties of Modern Armenian as well. Western Armenian, which is more conservative in this respect, forms the present tense by prefixing gə, a particle of unknown origin, to old forms, made up of the stem and personal endings. Eastern Armenian uses periphrastic forms: participle ending in -um (probably of locative origin) plus the copula em, es... ‘am, are…’. Thus, Old Armenian sir-em ‘I love’ is Western Armenian gə sir-em and Eastern Armenian sir-um em. The Old Armenian present tense has in both modern languages the value of a subjunctive. In Modern Armenian the passive is formed by means of the infixation -v-, as with sir-v-um em ‘I am loved’ (Eastern form).

In Old Armenian a declined adjective could be placed before or after a noun; in the modern language it may only precede a noun and has no case endings, as in Turkish and Georgian. Similarly, in Modern Armenian the genitive always precedes a noun. Postpositions are preferred to prepositions in Modern Armenian, unlike in Old Armenian. In other respects, Armenian word order is relatively free.