What is a Japanese intransitive verb?

Today, I’d like to discuss something I am still figuring out, so don’t expect a complete answer. Have you ever noticed how lots of verbs ending in -す are transitive? Stuff like 話す, 記す, etc. I am not counting compounds here, so e.g. 呼び出す does not count. I assumed this was just a heuristic, but I could not come up with pure verbs ending in -す that weren’t transitive.

Thankfully, a friend of mine (who happens to be fantastic at Japanese) mentioned 暮らす. This prompted a debate. Is 暮らす transitive or intransitive? After all, Jitendex/JMdict was saying the verb was intransitive, but a lot of people were saying that 暮らす is considered transitive, and multiple dictionaries (especially 古語 dictionaries) mentioned it being transitive. So what was it?

As usual, I asked on JSE and one well known member gave me a pretty interesting answer. Although there are verbs ending in -す that are intransitive, it is not the majority. Examples include 押す and 指す. In the answer, they mentioned that this might be because -す verbs are often part of transitive/intransitive pairs, and linked to a Wikipedia article discussing these pairs.

The definition on there was kind of interesting. I quote Wiktionary here:

A Japanese verb pair consists of a transitive verb and an intransitive verb sharing the same root, with the former serving as the causative/active voice, and the latter as the mediopassive voice.

So naturally, the next question that came to me was: “What the hell is a mediopassive voice?”

I understand what is meant by active voice. It’s the voice of action, i.e. the voice in which the subject does the action of the verb. I also understand the causative voice (in Japanese, it’s often seen as -(さ)せる, as in 食べさせる) which describes a subject causing something or someone to be or do something, or causing some state to change.

But what is the mediopassive voice? I think I understand the passive voice, where the subject is not the agent anymore (i.e., the person doing the action). But what is the mediopassive voice? First, I took a look at the Wikipedia page for passive, specifically the passive voice in Japanese. The article says Japanese does not have a middle voice, but a cheeky little [citation needed] seems to say it is not so clear cut.

Confused, I looked on Wikipedia and found a description of the middle voice. Here’s the definition given in the article:

[…] The subject of such middle voice is like the subject of active voice as well as the subject of passive voice, in that it performs an action, and is also affected by that action.

Mmmh, okay. Well, the article has an example which I think illustrates this better.

(4) The casserole was cooked in the oven. (passive voice)

Ok, I think this is pretty clearly passive.

(5) The casserole cooked in the oven. (middle voice)

So this is an example of the middle voice. The article continues:

For example, while the passive voice expresses a medium (goal) being affected by an external agent (actor) as in sentence (4), the middle voice expresses a medium undergoing change without any external agent as in sentence (5).

Mmmh. To convince us that this is truly different than the passive voice, the following two sentences are then compared:

(6) The casserole was cooked in the oven by Lucy (passive voice)

(7) The casserole cooked in the oven by Lucy (by-phrase ungrammatical when used with middle voice; asterisk () indicates ungrammaticality)

Ok. So this tells us what a middle voice is, but the initial article from before talked about the mediopassive, not the middle voice. So what’s a mediopassive? Apparently, it combines aspects of the passive and the middle voice. The article suggests the following as an example to something similar to it:

The book was not selling.

And indeed, the verb that describes this in Japanese (売れる) is intransitive. I am not convinced that this equivalence (intransitive Japanese verbs = mediopassive verbs) is totally correct, but that might just be because I didn’t look enough into it. I will do so and report back, because this is all kind of confusing to me. What do you think? What exactly makes intransitive verbs in Japanese have both passive and active aspects? Not to mention, certain passive constructions in Japanese can take intransitive verbs… Is that a passive acting on a mediopassive verb? My head is spinning.