The partitive is the way to express an indefinite plural quantity, as such it can be regarded as the plural of the indefinite article (Section 5.2). There are many English equivalents, such as “some…” or “a few…” There are several ways to express the partitive in Italian.
A. Di + the definite article (del, dello, dell’, della, dei, degli, delle) is the most common form of the partitive. It can be used for tangible things like clothes (dei vestiti = some clothes), intangible things like ideas (delle idee = some ideas), countable things like bags (degli zaini = some backpacks) and uncountable things like liquids (del succo = some juice):
Devono comprare delle cartoline. They have to buy some postcards.
Voglio sfogliare dei libri. I want to flip through a few books.
Ha comprato dello zucchero. He/she bought some sugar.
Hanno comprato del pane e delle arance. They bought some bread and some oranges.
Ho preso degli appunti. I took some notes.
Hanno delle idee interessanti. They have some interesting ideas.
With uncountable things like liquids (del succo = some juice; del latte = some milk), you have to use the singular construction; if you use the plural construction, the meaning changes to “some varieties of…” For example, dei succhi = some varieties of juice (apple, pear, etc.).
B. Un po’ di is a common form of the partitive. It, too, can be used with tangible and intangible things (like emotions), countable and uncountable things (like liquids). It is invariable. E.g.,
C’e` un po’ di vino. There’s some wine.
Vogliamo un po’ di cioccolato. We want some chocolate.
Lui ha un po’ di paura. He is a little afraid.
C. Alcuni/Alcune, alcuni can only be followed by masculine plural nouns (countable nouns); alcune can only be followed by feminine plural (countable) nouns.
Devo scrivere alcuni messaggi. I have to write a few messages.
Vuole saltare alcune riunioni. She wants to skip some meetings.
Abbiamo alcuni amici. We have some friends.
alcuni/alcune can also function as pronouns, i.e., “Some say that...”
Alcuni dicono che la Fiorentina vincerà il Campionato quest’anno.
Some say that (the team) Florence will win the championship this year.
Ho letto le tue lettere: alcune sono veramente belle.
I read your letters, some (of them) are really beautiful.
D. Qualche can only be followed by a singular noun (even though it always implies plurality!). It is invariable, e.g.,
Ho qualche amico a Pisa. I have a few friends in Pisa.
Ha bevuto qualche bicchiere di vino. He/she drank a few glasses of wine.
Ci manca qualche sedia. We are missing some chairs.
E. Omission of the partitive
The partitive is sometimes omitted from constructions:
Avete pane? = Avete del pane? = Do you have bread?
Berrei acqua. = Berrei un po’ di acqua. = I would drink some water.
The partitive is not used in negative sentences:
Noi non beviamo caffè. We don’t drink (any) coffee.
Lei non ha libri. She doesn’t have (any) books.
A casa mia nessuno mangia carne. At my house, no one eats meat.