Lesson 19: Passive られる・あれる and so-called "transitive pairs"
Passive verbs exist to turn the logical object of a verb into the grammatical subject. Unlike てある, passives describe the action, rather than making a statement about an enduring state left by that action.
Five-form and one-form verbs form the passive in different ways. Five-form verbs take the negative stem and replace ない with れる, the passive suffix. One-form verbs take the one and only base and add ら, *then* add れる. Basically, for regular verbs, you replace the last u with an a and add れる, unlike negatives where one-form verbs drop the る entirely instead of just the u.
食べられる
殺される
殺された人間の死体 The dead bodies of people who were killed.
魚が食べられた The fish got eaten.
The person who logically performs an action is called the "agent". If you want to state the agent of a passive verb, you usually use に, but for certain phrases, から is also acceptable. This calls back to に being a general fallback for the secondary arguments of a verb.
魚が猫に食べられた The fish was eaten by a cat.
In grammar study, there's a concept of verbal "transitivity", which basically just has to do with whether the verb accepts a normal direct object or not. We already learned that "intransitive" verbs describe a state if you attach ている.
彼を教えた I taught him. (transitive)
彼が死ぬ He dies. (intransitive)
"Transitive pairs" are pairs of japanese verbs that represent the same action, but one is transitive, and the other is not. Unlike passives, intransitive verbs in a "transitive pair" don't usually accept marking an agent with に.
上げる to raise something
上がる for something to rise
見る to see
見える for something to be seen/visible