The voice of a verb indicates who is receiving the action of the verb (the subject or the object) and who is performing the action (the subject, the object, or some other complement). There were originally three voices: the active, middle, and passive. Latin, like English, retains only the active and passive voices.
The subject is the doer (agent) of the action. If the verb is transitive (takes a direct object) then the object receives the action.
The action of a transitive verb "goes over" onto its object; the subject does the action to the object. Ferio pilam. I hit the ball.
The action of an intransitive verb does not "go over" onto any object. It is merely an action which the subject performs. Curro. I run.
Some verbs can be either transitive or intransitive depending on how they are used. Movebo. I shall move. (intransitive) Movebo sellam. I shall move the chair. (transitive)
The subject receives the action. The agent of the action is put into the ablative if it is a thing, or is expressed by ab plus the ablative if it is a person. The passive voice is a way to avoid blame or responsibility for an action or to describe an action when the agent is unknown.
Virgis caedetur. He shall be beaten with sticks. (Virgis is an ablative of means. The passive is employed because no agent is provided to tell who will do the beating.)
Mordebar ab fele. I was bitten by a cat. (ab fele is the ablative of agent telling who did the biting. The passive is employed to emphasize that I was bitten, and to de-emphasize that a cat did it.)
Vasa rupta est. The vase was broken. (No agent provided. The passive is used to avoid responsibility for the act. The act "just happened.")
Taberna irrupta est. The store was broken into. (No agent provided. The passive is used because the agent is unknown.)
The middle voice is used of an action which the subject does to itself, for itself, or in its own interest. The middle verb originally had forms similar to the passive, but it could take direct objects or act as a reflexive.
Sometimes, passive verbs in Latin, especially deponents, retain a middle sense. When used as a middle, they can take accusative objects. This is sometimes called the accusative of respect or the Greek accusative.
Lavor. I wash myself. (Not just "I wash.") cinctus caput sertibushaving girded his head with wreaths (having been girded with respect to his head by means of wreaths)
Deponents are verbs which exist only in passive forms, but their meanings are active (passive in form, active in meaning). They have no forms with passive meanings except the future passive participle, and they can take direct objects.
A deponent verb has only three principal parts: the first principal part (normally the first person singular active indicative) is supplied by the first person singular passive indicative, the second principal part (normally the present active infinitive) is supplied by the present passive infinitive, the third principal part (normally the first person perfect active indicative) and the fourth principal part (normally the perfect passive participle or the supine) are combined and supplied by the perfect passive participle plus sum, that is, the first person singular perfect passive.
Moror, morari, moratus sumto delay moror = I delay (NOT "I am delayed"); morari = to delay; moratus sum = I delayed and so on.
Semi-deponents are formed normally in the simple tenses (present, future, and imperfect), but are deponent in the perfect tenses (perfect, future perfect, and pluperfect).
Semi-deponents have three principal parts: the normal first and second principal parts, and in place of the last two, a deponent principal part.
audeo, audere, ausus sumto dare audethe dares; audeturhe is dared
but ausus esthe dared
Semi-deponents are very rare. The three most common are: audeo, audere, ausus sum to dare fido, fidere, fisus sum to trust gaudeo, gaudere, gavisus sum to rejoice
renovata antediem undecim Kalendis Augustis MMDCCLV A.U.C. (ab urbe condita)