Difference between 'di cui' and 'delle quali'

Question

1. 'non condivido le ragioni di cui mi parli'

2. 'non condivido le ragioni delle quali mi parli'

Can anyone explain what the difference between (1) and (2) is?

According to me, there is no difference, but I'm under the impression that 'di cui' has a singular connotation, even if I cannot say that it is singular or that it is used more proficiently when it is referred to something perceived as singular.

Answer 1

Both OK, "di cui" (and "per cui", "in cui" etc.) is shorter and invariant therefore it's more commonly used in spoken language and sounds less formal. Sometimes using "le quali" or the other forms with gender and number ("i quali", "il quale", "la quale") clarifies which is the noun referenced by the subordinate sentence, e.g.

...la sconfitta di Napoleone, per cui ho pregato con tutte le mie forze.

Did I pray for Napoleon or for his defeat?

...la sconfitta di Napoleone, per la quale ho pregato con tutte le mie forze.

Now you know (but if Napoleon were a woman, you'd still be confused).

Answer 2

To give a brief answer I can say I'm not sure if there is a formal better way to be used, but in spoken language both forms are used and none of them is frowned upon. For my personal experience, always talking about spoken language, the plural form "delle quali" is quite more formal than the singular form "di cui", but it could also be a regional matter.

Answer 3

When used with complementi indiretti, cui stays for la quale, il quale, le quali, i quali.

La ragazza di cui ti parlavo è stata licenziata.

Di cui is not used only for the singular, nor implies the word is perceived as singular.

Answer 4

Both forms may be used interchangeably. In such a short sentence I'd prefer "di cui", while in a longer sentence like "non condivido le ragioni per le quali/per cui hai deciso di convocarmi stamattina" I'd prefer "delle quali", but I believe it's a matter of taste.