First of all, to preempt the inevitable question, no, this post isn't a part of the series the post a couple posts ago was. Like most posts on Q & Stuff, the topic of this post is just what I happened to be thinking about at the time I decided to write a post. The flavor of the day is adjectives.
For the purpose of this post, I'm going to define 'adjective' in the theoretical sense, meaning a way of specifying attributes or other things about nouns. Clearly this is a very important (I might go out on a limb and say essential) part of every language. However, the means by which the theoretical purpose of adjectives is accomplished in language is unusually variable between languages. I know of at least four strategies of performing this task, and bear in mind that linguistics is my hobby - not my profession no even an area of expertise. Of course, languages often mix and match - some attributes may use one strategy, other attributes use another; some attributes may even have multiple ways of being represented.
The most obvious to us (I'm assuming most or all reading this speak some Indo-European language as their native language) are true adjectives. True adjectives, as I'm defining them in this post, are words which serve uniquely as adjectives. They attach to and modify nouns, and can serve no other purpose - other purposes require different words entirely. For a few examples from this paragraph: 'obvious', 'true', 'different'.
I've also mentioned one other type of adjectives in the past: verbal adjectives, or (the more commonly used term) stative verbs. That is, verbs which represent states of being. Japanese has many such verbs, several examples of which I've given in the past: 'sugoi' ('to be incredible'), 'aoi' ('to be [the color] blue'), 'warui' ('to be bad'). As I mentioned previously, when you see a stative verb used in a true-adjective-like way (e.g. 'aoi hana' - 'blue flower'), what you are actually seeing is a relative clause structure ('flower which is blue').
However, there's a second subtype of this strategy. We just discussed verbs which have stative meanings in the active voice. What's much more common in English (though still not as common as true adjectives) is the use of passive voice verbs as adjectives; that is, the use of verbs which, in the active voice, are defined as an action, but have a stative meaning in the passive voice. Some examples in English: 'ruined' (from 'ruin'), 'afraid' (from the archaic verb 'affray'), 'enlightened' (from 'enlighten'), etc. Interestingly, Japanese does not like this, and will use warped structures to keep verbs used as adjectives in the active voice (from one of my Japanese books: 'nansen ni atta suifu' - literally 'sailor who met ship-wreck').
Next up is the strategy used primarily by Caia, though languages like Latin and Japanese also do things like this: the use of abstract nouns to modify other nouns in an attributive manner by means of an attributive indicator. Take the classic Japanese word 'baka'. This word is a noun, meaning 'idiot', 'stupidity', etc. (it's kind of vague). However, using the genitive/attributive particle 'na', 'baka' can be used to mean 'stupid', as in 'baka na koto' ('stupid thing'). Latin places the attribute noun in the genitive case for this purpose (though note that the genitive also is used for other things, such as possession).
I chose to use this strategy in Caia for the purpose of simplicity. Adding in a third word type - true adjectives - would merely complicate things, and not offer a substantial benefit in some other way (there are a few true adjectives in Caia, but only things that are cumbersome to represent in the 'having [attribute]' paradigm - 'few', 'big', etc.). Initially I was hoping to have Caia represent most things in nouns, and use structures to represent adjectives and verbs (which would mean Caia has only one major word category), but I ultimately decided it would be too cumbersome to do that with verbs, and admitted a second major category.
However, just because those things are cumbersome to represent using nouns does not mean that representing them in such a way is impossible; it just requires a bit different strategy: the fourth I'll talk about. In contrast to using abstract nouns such as 'stupidity', this strategy represents attributes as concrete nouns possessing that attribute. For example, rather than having a word for 'stupidity', you have a word for 'idiot [someone stupid]' (although you could have both, as English does); to insult someone, you would then say "You are an idiot". I don't believe there are any languages you've ever heard of that use this strategy much, but there are real languages that do; and, as just demonstrated, other languages can use it in addition to other strategies. In theory, by combining this strategy and the last, you could create a language where all theoretical adjectives are represented as nouns.
In other news, my post history suggests I'm forgetting things I've done in the past.