The perfective aspect is equivalent to the aspectual component of past perfective forms variously called "aorist", "preterite", and "simple past". Although the essence of the perfective is an event seen as a whole, most languages which have a perfective use it for various similar semantic roles, such as momentary events and the onsets or completions of events, all of which are single points in time and thus have no internal structure. Other languages instead have separate momentane, inchoative, or cessative aspects for those roles, with or without a general perfective. Use of a perfective aspect, however, does not imply a punctiliar or short-lived action. It simply "presents an occurrence in summary, viewed as a whole from the outside, without regard for the internal make-up of the occurrence." 
The perfective aspect is distinguished from the imperfective aspect, which presents an event as having internal structure (such as ongoing or habitual actions), and from the prospective aspect, which describes impending or anticipated action.
Equivalents in English
English has neither a simple perfective nor imperfective aspect; see imperfective and perfective for some basic English equivalents of this distinction.
When translating from a language that has these aspects, they will sometimes be given separate verbs in English. For example, in Ancient Greek the imperfective sometimes adds the notion of "try to do something" (the so-called conative imperfect); hence the same verb root, in the imperfective (present or imperfect) and aorist, respectively, is translated as look and see, search and find, listen and hear (ἠκούομεν ēkoúomen "we listened" vs. ἠκούσαμεν ēkoúsamen "we heard").
Spanish is similar, with imperfect and preterite sabía "I knew" vs. supe "I found out", podía "I was able to" vs. pude "I succeeded", quería "I wanted to" vs. quise "I tried to", no quería "I did not want to" vs. no quise "I refused". Such distinctions are often highly language-specific.
Languages may mark perfective aspect with morphology, syntactic construction, lexemes/particles, or other means.
- Thai: the aspect marker ขึ้น /kʰɯ̂n/, grammaticalized from the word for "ascend," indicates a certain type of underconstrained perfective aspect when it follows a main verb
Perfective vs. perfect
The terms perfective and perfect are confused or interchanged in many grammatical descriptions. A perfect is a grammatical form used to describe a past event with present relevance, or a present state resulting from a past situation. For example, "I have come to the cinema" implies both that I went to the cinema and that I am now in the cinema; "I have been to France" conveys that this is a part of my experience as of now; and "I have lost my wallet" implies that this loss is troublesome at the present moment.
As English has a perfect, the distinction can be illustrated with the simple past standing in for the perfective. A perfect construction like "I've eaten" conveys the continued significance of that action, with implications such as "I'm full" or "you've missed dinner" depending on context. As such, it is ungrammatical to assign it a time in the past, such as "I've eaten yesterday". A perfective construction, however, has no such inherent implication of continued relevance, and as such "I ate yesterday" is perfectly grammatical; indeed, in languages which have a perfective, that is precisely the aspect which is used for such simple past events.
Traditional Greek grammar uses the term perfect in its modern sense. This was opposed to the aorist (past perfective in modern terms), which describes a unitary past action, and the imperfect (past imperfective), describing an ongoing past action. Latin, however, lost the distinction between perfective (aorist) and perfect, and for morphological reasons the single form covering both uses was called the "perfect". The two-way Latin distinction between imperfect and perfect carried over into the terminology of various modern languages, such as Slavic and the Romance languages, which have an aspectual distinction between imperfective and perfective. Here the word "imperfect" continues for the past imperfective, and the term "preterite" may be used for past perfective in contrast to the perfect.
Because of the common confusion of the terms perfect and perfective, various authors have tried to replace one or the other. Some use the Greek term 'aorist' for perfective, though this has the problem that it is commonly understood to mean specifically the past perfective. Others have replaced the perfect with anterior, though this can be ambiguous for those familiar with languages which have a true anterior tense. Less ambiguous is replacing 'perfect' with retrospective or resultative.
- Ancient Greek grammar: Dependence of moods and tenses
- Chinese grammar: Aspects
- Grammatical aspect in Slavic languages
- Bernard Comrie, 1976, Aspect, p 12. Comrie notes that aoristic may be confused with aorist, which is generally restricted to the perfective in the past tense, while the term perfective is commonly confused with perfect, which is not perfective at all.
- Fanning,B.M. Verbal Aspect in New Testament Greek at 97. Oxford:Clarendon, 1990.
- Koenig, J.-P., & Muansuwan, N. (2000). How to End Without Ever Finishing: Thai Semi-Perfectivity. JOURNAL OF SEMANTICS. 17, 147-184.