ILGUR: Italian Language, Grammar and Usage Resource

Italian verbs ending in -ire (also known as third conjugation) follow two different patterns. In the chart below, you have the standard pattern for -ire verbs, such as dormire:
There is a second class of -ire verbs which follow a different pattern, outlined below (such as the verb, preferire):

The pattern illustrated above is shown below with the verb, dormire (to sleep):

The second method of conjugation is shown below with the verb, preferire (to prefer) – note the -isc between the stem and the ending:
Do you see the differences between the two types of -ire verbs? When in doubt as to which pattern an -ire verb uses, consult a dictionary.

Below is a list of common -isc verbs that follow the same pattern as preferire:

agire – to act
ambire – to aspire
ammonire – to admonish
ardire – to venture
arrugginire – to rust
capire – to understand
chiarire – to clarify
colpire – to hit
costruire – to construct
demolire – to demolish
favorire – to favor
ferire – to wound
fiorire – to flourish
fornire – to supply
finire – to finish
guarire – to heal
inserire – to insert
impedire – to prevent
obbedire – to obey
patire – to suffer
percepire – to become aware of
proibire – to prohibit
pulire – to clean
punire – to punish
rapire – to kidnap
restituire – to give back
riferire – to relate, to refer
scolorire – to discolor
scolpire – to sculpt
sparire – to disappear
spedire – to send
stabilire – to establish
subire – to suffer
suggerire – to suggest
tossire – to cough
tradire – to betray
trasferirsi – to move
unire – to unite

There are some verbs that can follow either pattern:

aborrire – to abhor
applaudire – to applaud
assorbire – to absorb
inghiottire – to swallow
mentire – to lie
nutrire – to nourish
tossire – to cough