Why do French partitive articles (du and de la) and plural indefinite article (des) look like forms of the preposition de?
I am looking for some account that will bring an a-ha! moment to why de l'argent should mean some money or just money (as well as of the money) and des garçons should mean some boys or boys (as well as of the boys).
For now, I use the trick of inserting an invisible a quantity before de l'argent and a group before des garçons. ("Well, de l'argent > a quantity of money > some money, a-ha!")
So the answer could be about historical development, some deep psychological truth, or anything else to promote that sense of inevitability and rightness.
For what it is worth, I've noticed this pattern.
NOM. SG. - GEN. SG. - NOM. PL.
un (le) garçon - d'un (du) garçon - des garçons
boy - boy's - boys
puer - pueri - pueri
πατήρ - πατρός - πατέρες
Of course I am choosing words for which the pattern works, and it may not be all that striking in full tables. (Also, per comments below,I note that d'un garçon is not called a genitive.)