Estonian is a language with many cases, employing 14 productive ones. By comparison: Russian has six, German four and English only two cases. The meaning conveyed by case endings in Estonian is expressed by prefixes in English and many other languages.

Despite the large number of cases, the Estonian language lacks the ordinary object case, the accusative, which is common among the Indo-European languages. The direct object in Estonian is expressed by the nominative, genitive or partitive, in the singular, and by only the nominative or the partitive in the plural. Using the genitive object in the singular and the nominative object in the plural, marks the totality and finiteness of the action directed at that object. The usage of the partitive case expresses the partiality or unfinished nature of the action.

Thus the sentence:

means that Peeter was writing a poem, but it is not known whether he finished it.

Whereas:

denotes a finished action, with the poem ending up completed.

In a negative sentence, however, the Estonian language allows only the partitive (partial object):

The nominative object in Estonian is used for example in imperative mood:

Whereas in semantic cases, each case is marked by a certain ending, it is quite usual in grammatical cases that the nominative and genitive case, sometimes also the partitive case, has no case ending. On occasions, all three cases are the same in the singular, and can be distinguished only in the plural.

The case endings are the same in singular and plural, the plural is distinguished by suffixes:

Declension does not depend on word class - nouns and adjectives are declined in the same way. At the same time, the adjective always agrees with the primary word in number. It agrees with the primary word in ten productive cases out of 14.

Due to the phonemic alternation (gradation), the word's stem is sometimes unrecognisable vis-à-vis the nominative case as given in dictionaries, e. g.: