Nouns and adjectives generally inflect by gender (masculine and feminine, with only some instances of vestigial neuter) and number (singular and plural). Inflection patterns are similar for the two categories:
General noun and adjectival endings for number and gender
il capello nero , i capelli neri ("the black hair")
la bella macchina, le belle macchine ("the beautiful car(s)")
Masculine and Feminine
il/la comandante intelligente , i/le comandanti intelligenti ("the smart commander(s)")
l'atleta entusiasta, gli atleti entusiasti ("the enthusiastic athlete(s)")
All Nouns ending with a stressed vowel
singular = plural
la città, le città ("the town(s)")
il/la manager trendy, i/le manager trendy ("the trendy manager(s)")
In the last two examples, only the article carries information about gender and number.
The Italian hard and soft C and G phenomenon leads to a few spelling/pronunciation peculiarities in certain cases:
Words in -cio and -gio form plurals in -ci and -gi, e.g. bacio / baci ("kiss(es)")
Words in -cia and -gia have been a point of contention; according to a commonly employed rule, they:
form plurals in -cie and -gie if the final letter before the suffix is a vowel: camicia, camicie ("shirt(s)"); ciliegia, ciliegie ("cherry"/"cherries").
form plurals in -ce and -ge if the final letter before the suffix is a consonant: frangia, frange ("fringe(s)"); faccia, facce ("face(s)").
when the i is stressed, it always remains in plural: farmacia / farmacie ("chemist's shop(s)"), nevralgia / nevralgie ("neuralgia(s)").
Words in -co and -go behave quite irregularly: "the grammarians are skeptical of any attempt at giving a ruling about this area". There are only partial, empirical rules of thumb:
plurals are formed with -chi and -ghi if the last letter before the suffix is a consonant or a stressed vowel: fungo / funghi ("mushroom(s)"), stecco / stecchi ("stick(s)"), mago / maghi ("magician(s)"), fuoco / fuochi ("fire(s)")
plurals are formed with -ci and -gi if the last letter before the suffix is an unstressed vowel: comico / comici ("comedian(s)"), medico / medici ("physician(s)")
in words ending with -logo suffix, the plural is usually in -gi when -logo means "expert" or "student", corresponding to English -logist (e.g. archeologo / archeologi, "archaeologist(s)"), while it is in -ghi when it means "speech" or "reasoning", corresponding often to English -logue/-log (e.g. catalogo / cataloghi, "catalogue(s)").
there are exceptions such as amico / amici ("friend(s)"), greco / greci ("Greek(s)"), valico / valichi ("mountain pass(es)"), carico / carichi ("cargo(s)").