So, I'm attempting to evade work (again), and was struck by another random thought. I mentioned previously that Japanese and Korean adjectives are really intransitive verbs, which use relative clause structure to act as adjectives. I also mentioned that this seemed to be an integral part of Korean (e.g. the suffixes for adjectives and verbs are the same), while there's some evidence to the contrary in Japanese - adjectives have different suffixes, all but one of which have the form -k_, leaving the possibility that Japanese adjectives were true uninflected adjectives at one point, and had some suffix beginning in k affixed to them.
Well, there's a linguistic principle known as sprachbund. That's German for "binding of languages" ('sprach' is the Old English word for 'speak', and is still used in German). This is the principle that, when you have two or more languages in contact for a large period of time (and, especially, when there is a high degree of multilingualism in the population), the syntax (word order) of unrelated languages will come into sync. Other things also happen, such as word borrowing and language mutation, but those are beside the point.
What if, at some point in the past, Japanese and Korean (for the purpose of this hypothesis, we'll assume the languages are unrelated; the relation of the two - or lack thereof - is still in dispute, so this is not a radical assumption) populations mixed extensively. It's possible that Japanese acquired the Korean syntax of adjectives, transforming Japanese adjectives into intransitive verbs.
If this were the case, it's possible Japanese acquired other aspects of Korean, as well. For example, I saw in one book from the early 1900s that you could use the '[subject] [verb]' form in Japanese as well as the modern forms '[topic] wa [verb]' and '[subject] ga [verb]' ('wa' and 'ga' mark the topic and subject, respectively; at least in these forms, they do) at one point in the past, whereas in current books you only see the 'wa'/'ga' forms. It's interesting to wonder if Japanese might have picked up the topic and/or subject particles from Korean; especially so considering that 'ga' originally meant something completely different, and has been crudely repurposed into the subject particle, in a downright bizarre manner. Though you should take that idea with a grain of salt, as I haven't researched that possibility at all, and don't even have the original book I read about that in anymore (returned it to the library).
In other news, I just lost contact with my computer at work (more than a thousand miles away, on a holiday weekend). I guess that means work's done for this weekend.
UPDATE: Okay, got a reply from a Japanese-speaking classmate (naturally, as I do most of my blogging on a whim, I didn't wait for a reply to the e-mail I sent before posting :P ). He says that the "[subject] [verb]" form is still used in informal speech. So that probably rules out my second item of speculation. I'm still interested in whether there is any truth to my Korean adjectives hypothesis, though.