Aspect is the less famous partner of tense. Where grammatical tense systems deal with whether an event is objectively in the past, present, or future, aspect systems are concerned with fuzzier questions such as whether it is in the foreground or background of the narrative. Although it has traditionally been confused with tense, or at best treated as an obscure variant, in worldwide terms it's tense that's relatively minor – a good proportion of languages don't have any special tense marking, while languages similarly lacking in aspect marking are rare (although as it happens the one good example is German). Even Mandarin Chinese, otherwise uninflecting, has affixes for flagging aspect.
Different languages concentrate on marking different aspectual oppositions, but the most basic one is the distinction between perfective and imperfective (not to be confused – some hope! – with perfect vs. imperfect):
- an individual event given the spotlight, often implying that this action was completed as a single step in the narrative. Example: I got in my van, drove to the city, and met them.
- a general state viewed as the frame to the narrative (seen from “inside” and emphasising its internal structure). Example: As I drove the rain was still getting heavier.
Those two example sentences might be describing the same drive from alternate perspectives; the difference is a matter of narrative emphasis rather than objective scheduling. The languages of the Slavic family make considerable use of this distinction, but they signpost it in an unusually messy way: each verb in the dictionary is one of a canonical perfective vs. imperfective pairing, like Russian skazatʼ/govoritʼ = “to speak” or napisatʼ/pisatʼ = “to write”. They're often distinguished by prefixes, but it's an irregular, seemingly derivational* process, unlike the simple inflectional alternation common in other aspect‐marking systems.
Plenty of other occasionally used aspectual oppositions exist; here are some summaries (but bear in mind that you could write entire books about the subtle details):
- DYNAMIC vs. STATIVE
- more a matter of different kinds of word in the dictionary (“lexical aspect”) than of different uses of a given verb. Dynamic situations necessarily involve change, while statives deal with ones that naturally persist (and may even be a special category of adjectival verbs).
- EPISODIC vs. HABITUAL vs. GNOMIC
- (situations viewed as) isolated incidents, regular customs, or universal truths; occasionally marked by regular inflections, though never (as far as I know) a systematic three‐option alternation.
- INCEPTIVE vs. PROGRESSIVE (or CONTINUOUS) vs. CESSATIVE
- presents an event as (suddenly) starting, as ongoing/recurring (“I am driving”), or as coming to an (abrupt) end; this can easily be mistaken for tense, but each one may be set in the past, present, or future.
- PERFECT (vs. IMPERFECT)
- perfect is just a traditional bad name for retrospective (or sometimes even for perfective); several continental European languages have further muddled the situation by recycling their perfect construction as a plain past tense. The “imperfect” is just whatever's left over.
- PUNCTUAL vs. DURATIVE
- distinguishes (things presented as) sharply delimited, momentary events from more prolonged or open‐ended ones. Durative verbs are often stative and atelic, but we're sinking! for instance is neither.
- RESULTATIVE (or RETROSPECTIVE vs. PROSPECTIVE)
- highlights the immediate present implications rather than the events themselves; for instance where it broke is simply past tense, it has broken has resultative overtones implying that it remains unfixed. The same idea can apply either to (usually recent) past or (imminent) future.
- SEMELFACTIVE vs. FREQUENTATIVE (or ITERATIVE)
- one‐shot as opposed to repeated events; Old English had a frequentative suffix still visible in pairs like spark/sparkle.
- TELIC (or COMPLETIVE) vs. ATELIC
- divides processes with an inherent goal or end‐point (swam the river) from ones that can just carry on unlimitedly (swam backstroke). Where this is inflectional rather than lexical aspect (and/or if it also implies a cessative) it tends to be labelled as “completive”. This doesn't cover the idea of trying and failing, which is usually treated as imperfective.
English sentences are often ambiguous with regard to aspect, and when they do mark it, it's usually by way of optional periphrastic forms, as in you ARE going/you HAVE gone/you USED TO go. None of those constructions are anything you'd want an auxiliary language to copy, but the general idea of using catenated verbs as in fini iri = “to finish going” and kutimi iri = “to be accustomed to going” could easily be expanded to cover all of the above shades of meaning via one standard mechanism. What Esperanto uses instead is a mess of different bolted‐on afterthoughts.
- ‐ad: in cases like ternadi = “to sneeze repeatedly” this is a frequentative affix, and the same is true in nouns derived from those verbs (ternado = “repeated sneezing”). In other cases it's more of a durative, emphasising uninterrupted continuity: marŝadi = “to keep walking”. But usage authorities disagree about what happens in the special case of a verb that is itself derived from a noun‐root (such as krono/kroni = “a crown/to crown”). Some say that here, exceptionally, adding ‑ado simply turns it back into a plain deverbal noun: kronado “a coronation, an act of crowning”. Likewise for fulmado: is it “continual flickers of lightning” or a single “lightning‐flash”?
- ek‐: a prefix specially designed to be used for aspectual purposes, which is a good start, but then it all goes wrong. Half of the time, it's an inceptive, as in ekdormi = “to fall asleep”; the other half of the time it's a punctual marker, as in ekvidi = “to glimpse briefly”. You have to learn each individual case to be sure that these coinages don't mean “to doze off momentarily” and “to begin watching”; the only reason they share the same prefix is that both functions are associated with Slavic perfectives. Being a derivational affix, it also gets to occur as a word in its own right, but eki only seems to be a synonym for komenci.
- el‐: a prepositional prefix literally meaning “out from” – hence eliri = “to exit, head off out”. Equivalent Slavic prefixes such as Russian vy‑ can function as a telic marker, as in vyuchitʼ = ellerni = “to learn by heart, master fully”. Like the above, however, this isn't an inflection of the verb; it's a purely derivational process, creating a new dictionary entry alongside kunlerni = “to learn together” and relerni = “to relearn”.
- ‐iĝ: this is sometimes mentioned as an (“inchoative”) aspect marker, but the difference between grandi = “to be big” and grandiĝi = “to grow, become big” is an inherent difference in the situation being described (tenuously related to stative/dynamic) rather than a matter of grammatical aspect.
- ‐int‐/‐ant‐/‐ont‐: the Fundamento (in most translations) represents these as simply “past”, “present”, and “future” participles, which is a bare‐faced lie; what they really mark at least some of the time is (past) retrospective, (present) progressive, and (future) prospective, and the compound constructions created using them are distinguished from the simple tensed verbs by their taken‐for‐granted aspectual implications. For instance, it's true to say that la suno fariĝos ruĝa giganto = “the sun will become a red giant”, but that's not the same as saying that la suno estas fariĝonta ruĝa giganto = “the sun is about to become a red giant”.
- ‐it‐/‐at‐/‐ot‐: in the case of the passive participles, the absence of any one‐word tensed equivalents for them to contrast with resulted in decades of argument over whether the distinction between these three forms was primarily a matter of tense or aspect. “Aspectism” was eventually declared orthodox by the Academy of Esperanto (at least for ‑it‑), but nobody seems to be telling modern learners about this – I've heard from people who assumed the opposite and had no idea they were heretics.