22. Perfect.

The perfect aspect is a grammatical aspect, which refers to a state resulting from a previous action (also described as a previous action with relevance to a particular time, or a previous action viewed from the perspective of a later time).

For example, "I have gone to the cinema" implies both that a previous action happened ("I went to the cinema") and that a current state resulted ("I am now in the cinema"). This differs from the simple "I went to the cinema", which implies only that an action happened, with no relevance to the present. The form "I have gone" is referred to as a present perfect, meaning present tense, perfect aspect. (It is considered present tense, not past tense, since the resulting state is in the present.)

23. Aspect.

In linguistics, the grammatical aspect of a verb defines the temporal flow (or lack thereof) in the described event or state. For example, in English the difference between I swim and I am swimming is a difference of aspect.

Aspect, as discussed here, is a formal property of a language. Some languages distinguish a large number of formal aspects (see the list below), while others distinguish none at all. Even languages that do not mark aspect formally, however, can convey such distinctions, if important, by the use of adverbs, phrases, serial verb constructions or other means.

Present Simple (not progressive/continuous, not perfect; simple): "I eat"

Present Progressive (progressive, not perfect): "I am eating"

Present Perfect (not progressive, perfect): "I have eaten"

Present Perfect Progressive (progressive, perfect): "I have been eating"

...and for the past tense:

Past Simple (not progressive/continuous, not perfect; simple): "I ate"

Past Progressive (progressive, not perfect): "I was eating"

Past Perfect (not progressive, perfect): "I had eaten"

Past Perfect Progressive (progressive, perfect): "I had been eating"

Another aspect that does survive in English, but that is no longer productive, is the frequentative, which conveys the sense of continuously repeated action; while prominent in Latin, it is omitted from most discussions of English grammar, as it suggests itself only by Scandinavian suffixes no longer heard independently from the words to which they're affixed (e.g., "blabber" for "blab", "chatter" for chat", "dribble" for "drip", "crackle" for "crack", etc.).

24. Voice.

In grammar, voice is the relationship between the action or state expressed by a verb, and its arguments (subject, object, etc.). When the subject is the agent or actor of the verb, the verb is said to be in the active voice. When the subject is the patient, target or undergoer of the action, it is said to be in the passive voice.

For example,

The cat ate the mouse

is active, but

The mouse was eaten by the cat

is passive.

In a transformation from an active voice sentence to an equivalent passive voice construction, the subject and the direct object switch places. The direct object is promoted to subject, and the subject is demoted to an optional complement. In the above examples, the mouse is the direct object in the active voice version, the subject in the passive version. The subject of the active voice version, the cat, becomes part of a prepositional phrase in the passive version of the sentence, and could be left out entirely. In the English language, the passive voice is periphrastic; that is, it is not a single word form, but rather a construction making use of other word forms. Specifically, it is made up of a form of the auxiliary verb to be and a past participle of the main verb. In other languages, such as Latin, the passive voice is simply marked on the verb by inflection: the passive voice uses different verb endings than the active voice.