(Part I) Please allow me to introduce the subject one step at a time. a1) Ho letto un libro che sta in questa biblioteca. (also: che e` in questa biblioteca) means: a2) Ho letto esattamente 1 libro che sta in questa biblioteca. (I read EXACTLY one book that is in this library) And so on, for any other numbers, like b1) Ho letto cinque libri che sono in questa biblioteca. b2) I read EXACTLY five books that are in this library. Note also that the plural article by itself in many cases (NOT in all case, see below) has an implied meaning of 'ALL/. c1) Ho letto I libri che sono in questa biblioteca. c2) I read ALL the books that are in this library. What happens if you want to express the meaning of a not specific number but more than one, and not all of the books? This is case where 'pronomi partitivi' or 'articoli partitivi' are useful to avoid long sentences. d1a) Ho letto dei libri che sono in questa biblioteca. Is a short way for saying: d2) I read more than one book, but not all that are in this library or d3) I read some of the books that are in this library The meaning of (d1a) could also be expressed as (d1b), (d1c): d1b) Ho letto ALCUNI librI che sono in questa biblioteca. d1c) Ho letto QUALCHE librO che sta in questa biblioteca.

The partitive articles are not originally articles but "compound preposition" (preposizioni articolate) used as articles. They are used mainly to substitute the non existent plural for the indeterminative articles (un, uno, una do not have a plural form) and they are used to indicate a part of something. For example :"ho letto dei libri / I read some books" it means I didn't read all the books but some of them. They are also used with singular nouns that don't have a specific quantity as for example: "mi passi del sale?" / can you give me some salt?" You don't say how much salt, but just "some" of it. The difference between degli and gli is that the first one is a partitive article, the second is a determinative one. As I already said tough, the partitive articles are not exactly articles, they are "made" by a simple preposition plus an article. It is a very long argument that involves articles and prepositions so I hope I was clear enough but if you need a better explanation feel free to contact me anytime. :)

(Part II) Examples: Vuoi delle penne? (Do you want SOME pens?) Si`, per favore, ne hai una verde e una rossa? Ti servono dei soldi? (Do you need SOME money?) Stai uscendo? Puoi comprare del pane per favore? Are you going out? Could you please buy SOME bread? In the last example, 'del' does not mean 'a number of', like 2, 3, 4 .., but a limited quantity of something. When the quantity to buy is implicit from the context, than you could also say: Puoi comprare IL pane? (what is needed by the family for one day) Devo comprare LA frutta ? Or: Vuoi che compro LA frutta? Quanta NE devo comprare? Here /ne/ is 'pronome partitivo' with the meaning 'of it'. How much should I buy 'of it' ? Forse delle altre persone scriveranno degli altri esempi. delle altre persone = some more people degli altri esempi = some more examples note: alcuni, qualche, qualcosa, qualcuno are also terms useful when expressing a part, and not the totality of something, but this would be another subject.