自他動詞

One of the stepping-stones on the route to learning Japanese that foreigners face is the difference between transitive and intransitive verbs. In English, a lot of verbs are the same in their transitive or intransitive forms -- context separates whether we speak of hanging something (transitive) or something hanging (intransitive).

Idle Speculation: I think this could be because Latin, Greek, and German all have oblique cases showing subject, direct object, and so forth, so having different verbs for action and state was a bit of a moot point. They also have auxiliary verbs for showing passive tenses. I don't know enough about Chinese and Japanese to know if some of these pairings are contractions of passive verbs, but that's what some of them look like.

</speculation>

In Japanese, many verbs come in transitive-intransitive pairs, called ¹jitadoushi (自他動詞). They use the same kanji for their root, but they have a different ending. Here are some examples:

aru → eru

Intransitive            Transitive           Kanji
ataru - (it) is hit     ateru - hit (it)       当
tomaru - (it) stops     tomeru - stop (it)     止

u → eru

Intransitive            Transitive           Kanji
aku - (it) is open      akeru - open (it)      開
sodatsu - (it) grows up sodateru - bring up    育

waru → eru

Intransitive            Transitive           Kanji
kawaru - (it) changes   kaeru - change (it)    変
tsutawaru - (it) sends  tsutaeru - send (it)   伝

... and so on. Most of the intransitive verbs are Godan and end in -u, whereas most of the transitive verbs are Ichidan and end in -ru.

This is where my theory about a passive contraction breaks down, because passive (and theoretically intransitive) verbs are Ichidan. Further proof that passivity and intransitivity are not the same thing.

One of the benefits of verb pairing is that by learning one verb, you learn two. Trying to memorize a group of verb pairs from one category at a time makes the job much easier than trying to learn verb pairs at random.

I'm told that proper usage of transitive and intransitive verbs is another one of the various gaijin tests that tell how much Japanese language and culture foreigners understand, like using chopsticks, or Japanese elevator etiquette.

²Other, less reliable jitadoushi rules:

ru → su
ku → su
eru → asu, yasu, or u
reru → su or asu
iru → osu

¹ Dr. Ben Bullock, "Alternative sci.lang.japan FAQ", http://www.csse.monash.edu.au/~jwb/afaq/afaq.html
² Kaiser, Ichikawa, et. al. Japanese: A Comprehensive Grammar ISBN 0-415-09920-X