Sapere means "to know" a fact or a piece of information, and with an infinitive it means "to know how to". It is the verb behind non lo so, "I don't know", one of the first phrases every learner needs.
Infinitive
sapere
English
to know; to know how to
Auxiliary
avere or essere
Past participle
saputo
Gerund
sapendo
Modal-type irregular verb. The present is short and irregular in every person except voi sapete: so, sai, sa, sappiamo, sapete, sanno. Notice how so, sai, sa and sanno rhyme with the present of avere (ho, hai, ha, hanno). The stem sapp- runs through the present subjunctive (sappia, sappiano) and the imperative (sappi, sappiate). The future and conditional drop the e of the infinitive: saprò, saprai, saprei. The passato remoto is irregular in three persons: seppi, seppe, seppero. The participle saputo and the imperfect sapevo are regular.
Sapere covers knowledge you can state: a fact (so che è sposato), an answer (sai dov'è la farmacia?), or a skill (sa suonare il piano). For people, places and things you are familiar with, Italian uses conoscere instead. Sapere is also the polite way to ask for information: saprebbe dirmi...? is the standard "could you tell me...?" in shops and at stations. In the passato prossimo it usually means "found out" or "heard", and with di it describes taste and smell: sa di limone, "it tastes of lemon".
Sapere takes avere: ho saputo, avevamo saputo. When sapere means "to be able to" and is followed by a verb that takes essere, careful Italian sometimes uses essere, mostly when a reflexive pronoun comes before sapere: non si è saputa difendere. Avere is always correct if you attach the pronoun to the infinitive: non ha saputo difendersi.
Sapere in context
Presente:Scusi, sa dov'è la stazione? (Excuse me, do you know where the station is?)
Presente:Mio figlio sa nuotare da quando aveva quattro anni. (My son has known how to swim since he was four.)
Passato Prossimo:Ho saputo solo ieri che Luca si è trasferito a Torino. (I only found out yesterday that Luca has moved to Turin.)
Imperfetto:Non sapevo che il museo fosse chiuso il lunedì. (I didn't know the museum was closed on Mondays.)
Futuro Semplice:Domani sapremo i risultati dell'esame. (Tomorrow we will know the exam results.)
Condizionale Presente:Saprebbe dirmi a che ora parte l'ultimo autobus? (Could you tell me what time the last bus leaves?)
Congiuntivo Presente:Voglio che tu sappia la verità. (I want you to know the truth.)
Imperativo:Sappi che puoi sempre contare su di me. (Know that you can always count on me.)
Common expressions with sapere
non lo so: I don't know. Italians usually include lo, "it". Non so alone is also correct, often before a question word: non so dove sia.
fammi sapere: let me know. From far sapere, "to let someone know". The formal version is mi faccia sapere.
che io sappia: as far as I know. Always with the subjunctive sappia: che io sappia, il negozio è aperto.
sapere di: to taste of, to smell of. Questa minestra sa di bruciato: "this soup tastes burnt".
saperla lunga: to know a thing or two, to be nobody's fool
chissà: who knows, I wonder. A fused form of chi sa: chissà se verrà, "I wonder if he will come".
Common mistakes
Conosco Maria da dieci anni., not So Maria da dieci anni. (I have known Maria for ten years.). Sapere never takes a person as its object. To know a person, a city or a restaurant, use conoscere. Sapere is for facts and skills: so dove abita Maria, "I know where Maria lives".
So parlare tre lingue., not Posso parlare tre lingue. (I can speak three languages.). English "can" covers both permission and learned skill. Italian uses potere for permission or possibility and sapere for a skill you have learned: so guidare, so cucinare, so parlare tre lingue.
What is the difference between sapere and conoscere?
Sapere is for facts, information and skills: so che hai ragione, sai cucinare? Conoscere is for familiarity with people, places and things: conosco Roma, conosci mio fratello? A quick test: if the object is a clause (che, dove, come, se...) or an infinitive, use sapere. If it is a person or a place, use conoscere.
Does sapere take essere or avere?
Avere: ho saputo, hai saputo, abbiamo saputo. Essere is possible only in a narrow case, when sapere means "to be able to" and a reflexive pronoun comes before it (non si è saputo trattenere). If you put the pronoun on the infinitive, avere is always correct: non ha saputo trattenersi.
What does ho saputo mean?
In the passato prossimo sapere usually means "I found out" or "I heard": ho saputo che vi sposate, "I heard you are getting married". To say you already knew something over a period of time, use the imperfect: lo sapevo, "I knew it".
Is sapere irregular?
Yes. The present (so, sai, sa, sappiamo, sanno), the subjunctive and imperative stem sapp- (sappia, sappi), the future and conditional stem sapr- (saprò, saprei) and the passato remoto seppi are all irregular. The participle saputo is regular.