Understanding the purpose of determiners/articles/demonstratives in language

Question

This was an interesting read:

Articles have developed independently in many different language families across the globe. Generally, articles develop over time usually by specialization of certain adjectives or determiners, and their development is often a sign of languages becoming more analytic instead of synthetic, perhaps combined with the loss of inflection as in English, Romance languages, Bulgarian, Macedonian and Torlakian.

Joseph Greenberg in Universals of Human Language describes "the cycle of the definite article": Definite articles (Stage I) evolve from demonstratives, and in turn can become generic articles (Stage II) that may be used in both definite and indefinite contexts, and later merely noun markers (Stage III) that are part of nouns other than proper names and more recent borrowings. Eventually articles may evolve anew from demonstratives.

Wondering if one could elaborate on this. I don't quite understand the second paragraph what some example sentences would look like for each stage. In this context, not sure what a demonstrative would be, vs. a generic article, definite/indefinite context, and noun markers.

I don't quite understand what follows as well:

Definite articles typically arise from demonstratives meaning that. For example, the definite articles in most Romance languages—e.g., el, il, le, la, lo — derive from the Latin demonstratives ille (masculine), illa (feminine) and illud (neuter).

The English definite article the, written þe in Middle English, derives from an Old English demonstrative, which, according to gender, was written se (masculine), seo (feminine) (þe and þeo in the Northumbrian dialect), or þæt (neuter). The neuter form þæt also gave rise to the modern demonstrative that. The ye occasionally seen in pseudo-archaic usage such as "Ye Olde Englishe Tea Shoppe" is actually a form of þe, where the letter thorn (þ) came to be written as a y.

So a definite article is something like the. This derives from a demonstrative like that. The demonstratives in Latin are listed above for example (ille, etc., not sure how many there are, if they are huge in number with conjugations like verbs, etc.). So that gets us [from Stage 0] to Stage 1. But not sure what Stage 2 and 3 are. Wondering if one could explain this in more depth. Hopefully from that it will provide a deeper understanding of the meaning and purpose of words like the and a.

Answer 1

Well, I explained the why it's useful in your other question so if you're asking about the process as curiousdannii said, that is you are asking about the grammaticalisation cycle, I could explain a little about the process.

1. Latin has a rich case system allowing free word order which is used as as a discourse marker; words encoding new or salient information tend to go at the end of the sentence)

2. For unrelated reasons, the case system collapses, so that word order becomes more rigid, which means there's pressure to find another way to solve the problem which was solved by the flexibility in word order before. Demonstratives are a natural candidate

3. The meaning of demonstratives weakens because they are now being used much more. So they are generally phonetically unstressed.

4. We now have unstressed morphemes adjacent to semantically loaded lexemes. These have a strong tendency to cliticise, which is what happened in Romanian and others.

A similar story goes for Germanic languages too, and probably other language families.