ILGUR: Italian Language, Grammar and Usage Resource

Some prepositions in Italian contract with the definite article. These prepositions are called preposizioni articolate and apply to the following prepositions:

Con (with) may combine with the definite article, but this is usage is becoming non-standard. Per (for - has other idiomatic meanings) may combine with the definite article, but this is seen only in archaic Italian and some poetry. Tra and fra (among, between) never combine with the definite article.

MOLTO IMPORTANTE: The preposition and definite article always combine. When in doubt, it’s a good idea to assume it is to be combined. However, there are idiomatic exceptions where the definite article is omited or not combined with the preposition (unless it is modified by adjectives or other prepositional phrases). Below are some common expressions where the definite article is not combined with the preposition. Often there is very little rhyme or reason to this so take your cue from native speakers and Italian writing.

TAKE NOTE: When the noun in the expression below are modified, then the definite article is combined with the preposition. Some examples are shown below.

• con disappunto
  to the disappointment 

   

• in casa
  at home; in the house
  
• in classe (but nella piccola classe)
  in class
  
  
• in bagno
  in the bathtub, in the tub
  
• in biblioteca (but nella biblioteca dell’università)
  in the library 

• in bolletta
  in the bill 

• a casa
  at home 

• in campo
  in the field 

• in città
  in the city 

• in cucina
  in the kitchen
  Typically, when referring to location within a home, the definite article is not used:
  Siamo in salotto. = We are in the drawing room.
  
• in chiesa
  in church
  
• a letto
  in bed
  
• in caserma
  in the barracks 

• in montagna
  in the mountains
  
• in poltrona
  in the chair
  
• in ufficio
  at the office
  
• in banca
  in the bank, at the bank
  
• a teatro
  at the theatre
  
• in piscina
  in the pool
  
• in discoteca
  at the disco
  
• in ospedale
  at the hospital, in the hospital 

• in qualità
  in the quality 

• in tribunale
  in court, at court, before the court 

• una mancanza di, la mancanza di
  a lack of, the lack of
  you will often see this expression where the prepositon is simply followed by the noun
  i.e.: una mancanza di soldi, la mancanza di comunicazione 

• in agguato
  in/into a trap; in/into an ambush