In Slavic languages, only one nearly universal type of aspectual opposition forms two grammatical aspects: perfective and imperfective (in contrast with English, which has several aspectual oppositions: perfect vs. neutral; progressive vs. nonprogressive; and in the past tense, habitual ("used to ...") vs. neutral). The aspectual distinctions exist on the lexical level - speakers have no unique method of forming a perfective verb from a given imperfective one (or conversely). Perfective verbs are most often formed by means of prefixes, changes in the root, or using a completely different root (suppletion). Note, however, that possessing a prefix does not necessarily mean that a verb is perfective. Contrast between a perfective and an imperfective verb may be also indicated by stress, e.g. Russian perfective осы́пать, imperfective осыпа́ть (to strew, shower, heap upon something).
With a few exceptions each Slavic verb is either perfective or imperfective. Most verbs form strict pairs of one perfective and one imperfective verb with generally the same meaning. However, each Slavic language contains a number of bi-aspectual verbs, which may be used as both imperfective and perfective. They are mainly borrowings from non-Slavic languages, but some native verbs also belong to this group. As opposed to them, mono-aspectual verbs are mainly native. There are mono-aspectual imperfective verbs without perfective equivalents (among others, verbs with the meaning "to be" and "to have") as well as perfective verbs without imperfective equivalents (for instance, verbs with the meaning "become ...", e.g. "to become paralyzed", etc.).
The perfective aspect allows the speaker to describe the action as finished, completed, finished in the natural way. The imperfective aspect does not present the action as finished, but rather as pending or ongoing.
An example is the verb "to eat" in the Serbo-Croatian language. The verb translates either as jesti (imperfective) or pojesti (perfective). Now, both aspects could be used in the same tense of Serbian. For example (omitting, for simplicity, feminine forms like jela):
| Example | Tense | Aspect |
|---|---|---|
| Ja sam jeo/ Ja сaм јеo | past | imperfective |
| Ja sam pojeo/ Ja сaм појеo | perfective | |
| Ja sam bio jeo/ Ja сaм био jeo | pluperfect | imperfective |
| Ja sam bio pojeo/ Ja сaм био појеo | perfective | |
| Ja ću jesti/ Ja ћy jecти | future | imperfective |
| Ja ću pojesti/ Ja ћy пojecти | perfective |
Ja sam pojeo signals that the action was completed. Its meaning can be given as "I ate (something) and I finished eating (it)"; or "I ate (something) up".
Ja sam jeo signals that the action took place (at a specified moment, or in the course of one's life, or every day, etc.); it may mean "I was eating", "I ate" or "I have been eating".
The following examples are from Polish.
Imperfective verbs mean:
Perfective verbs can refer to the past or to the future, but not to present activities – an activity happening now cannot be ended, so it cannot be perfective. Perfective verbs convey:
Most simple Polish verbs are imperfective (as in other Slavic languages), ex. iść 'to walk, to go', nieść 'to carry', pisać 'to write'. But there are also few simple perfective verbs, ex. dać 'to give', siąść 'to sit down'. There exist many perfective verbs with suffixes and without prefixes, ex. krzyknąć 'to shout', kupić 'to buy' (cf. the imperfective kupować with a different suffix).
Numerous perfective verbs are formed from simple imperfectives by prefixation. To create the perfective counterpart, verbs use various prefixes without any clear rules. The actual prefix can even depend on a dialect or special meaning. For example: the perfective counterpart to malować is pomalować when it means 'to paint a wall; to fill with a color', or namalować when it means 'to paint a picture; to depict sth/sb'.
Besides the strict perfective equivalent, a number of other prefixed verbs may be formed from a given simple imperfective verb. They all have similar but distinct meaning. And they form, as a rule, their own imperfective equivalents by means of suffixation (attaching suffixes) or stem alternation. Example:
A number of verbs form their aspectual counterparts by simultaneous prefixation and suffixation or by suppletion, ex. (the first one is imperfective) stawiać - postawić 'to set up', brać - wziąć 'to take', widzieć - zobaczyć 'to see'.
Special imperfective verbs express aimless motions. They are mono-aspectual, i.e., they have no perfective equivalents. They are formed from other imperfective verbs by stem alternations or suppletion, ex. nosić 'to carry around' (from nieść), chodzić 'to walk around, to go around' (from iść 'to go, to walk'). However, when such a verb gets an aim anyway, it becomes iterative: chodzić do szkoły 'to go to school'.
Other iteratives build another group of mono-aspectual imperfective verbs. They are formed from other imperfective verbs, including the previous group: chadzać 'to walk around usually (from chodzić), jadać 'to eat usually' (from jeść 'to eat'). Both groups are not too numerous: most Polish verbs cannot form iterative counterparts.
Perfective verbs that express activities executed in many places, on many objects, or by many subjects at the same time, and those that express actions or states that last some time, have no imperfective counterparts. They are formed with the prefix po- (which can have other functions as well).
States and activities that last for some time can be expressed by means of both imperfective and perfective verbs: cały dzień leżał w łóżku 'he was in bed all day long' (literally: 'he lay in bed') means nearly the same as cały dzień przeleżał w łóżku. The difference is mainly stylistic: imperfective is neutral here, while using perfective causes stronger tone of the statement.
Aspect in Slavic is a superior category in relation to tense or mood. Particularly, some verbal forms (like infinitive) cannot distinguish tense but they still distinguish aspect. Here is the list of Polish verb forms formed by both imperfective and perfective verbs (such a list is similar in other Slavic languages). The example is an imperfective and a perfective Polish verb with the meaning 'to write'. All personal forms are given in third person, masculine singular, with Russian analog:
The following may be formed only if the verb is imperfective:
One form may be created only if the verb is perfective, namely:
Aspect in Russian is often discussed in terms of grammatical aspect or lexical aspect. Grammatical aspect is a temporal understanding of aspect where the aspect is determined according to the relationship between the reference time and event time. In aspect no reference is made to speech time; however, speech time is included when determining the tense.
Grammatical Aspect: Perfective Aspect obtains when the event time occurs before the reference time (E > R). Such an example might be Иван прочитал книгу. Imperfective Aspect Obtains when the event time equals the reference time (E=R). Such an example might be Иван читал книгу.
Lexical Aspect (Aktionsart) Lexical Aspect in Russian often uses a semantic analysis of lexical items. Within this perfective, lexical items entail boundedness, completion, and telicity. Imperfective lexical items ential non-boundedness, referring to states and ongoing activities.