Partitive Genitive

Question

I've read a bit about the partitive genitive in Russian, used in expressions such as "кусок сахару", "чашка чаю".

However, the sources I use usually label this declension as facultative, mainly literary.

1. So, are "кусок сахару" and "чашка чаю" just alternatives to "кусок сахара" and "чашка чая" respectively?

2. Second question: It's told that the partitive genitive, when used to talk about an indefinite amount of a commodity, is analogous to the French usage of de / du / de la.

In French it's common to say "Je veux du thé" ("I want [an indefinite amount of] tea").

Has partitive genitive in Russian the same function here? Like, "Я хочу чаю", "Я хочу сыру", in order to express desire for an indefinite amount of a feeding commodity?

3. As far as I know, the verb "хотеть" is followed either by accusative (when referring to concrete nouns in general) and genitive (regarding abstract nouns such as in the expression "Я хочу мира", or negation).

When referring to a commodity such as чай, сыр, сахар, is it better to use accusative ("Я хочу чай") or genitive? If genitive, may I use "Я хочу чая" and "Я хочу чаю" interchangeably, or just чаю?

Answer 1

1. So, are "кусок сахару" and "чашка чаю" just alternatives to "кусок сахара" and "чашка чая" respectively?

By and large they are. However this relates to your question # 2 and so some distinction could be drawn.

2. Has partitive genitive in Russian the same function here? Like, "Я хочу чаю", "Я хочу сыру", in order to express desire for an indefinite amount of a feeding commodity?

I would say so. Because if a limited quantity substance was mentioned earlier (a pack of tea you have, a brick of cheese you bought) it would most likely be pointed at with regular genitive. It would serve as a kind of definite article "the". Partitive genitive in such case would create a mixed message. To illustrate

-Хочу сыру (I want some cheese)
-Так у тебя же в холодильнике лежит целая пачка (But you do have a pack in the fridge)

But i doubt anyone will be able to put in words the confusion it would create. Overall this is marginal, the slight difference in connotation will rather be simply dismissed by the interlocutor.

3. When referring to a commodity such as чай, сыр, сахар, is it better to use accusative ("Я хочу чай") or genitive? If genitive, may I use "Я хочу чая" and "Я хочу чаю" interchangeably, or just чаю?

No, genitive is the normative case here, but again the type of genitive may depend on the message the speaker wishes to convey as pointed out in the explanation above. Generally however they're interchangeable.

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^{As a side, all the odd cases, unfortunately in my opinion, aren't formally taught in school and most people have no knowledge of their existence despite using them in their speech. So because of not being the formal part of modern Russian language rules set, they aren't well protected from attrition and are prone to corruption or falling out of use, which i think is what's happening in particular to genitive partitive.}