Ablative of Agent
In the active voice the subject (nominative) performs the action of the verb. In the passive voice, the action of the verb is performed upon the subject (still nominative). To indicate who or what was doing the verb, Romans used the ablative of agent construction.
You already know half of the ablative of agent, the ablative of means which describeds the means by which something is done; e.g.
When the agent of a passive verb is a human or divine being, (as opposed to inanimate agents like "rains"), the ablative of agent is expressed by "ab" plus the ablative.
note - You may use the form "ä" before words that begin with consonants. You may use the form "ab" before words that begin with either vowels or consonants. You must use "ab" before words that begin with vowels.
You should be able to transform any active transitive verb into a passive construction:
In the passive version of this sentence: