Savoir: Knowing Facts, Knowing How

Savoir is one of the most useful verbs in French, and one of the most misused by English speakers. It covers two distinct meanings that English keeps separate: knowing a fact (je sais qu'il vient, "I know he's coming") and knowing how to do something (je sais nager, "I know how to swim / I can swim"). The second use is what makes savoir a modal verb — like pouvoir, vouloir, devoir, it can take a bare infinitive and shift the meaning of the action it precedes.

This page drills the full paradigm — including the unique present stem sai-/sav-, the distinctive subjunctive sache that you'll meet in fixed expressions long before you study the subjunctive proper, and the famous past participle su — and walks through the four main uses: knowing facts, knowing information through clauses, knowing how to (skill), and the polite savoir with subjunctive triggers. It also covers the most consequential split in the French verbal system for English speakers: the line between savoir and connaître, which both translate as know in English but cover different territories in French.

Full conjugation

Savoir is irregular in nearly every tense. The infinitive savoir and the present stem sav- both descend from Vulgar Latin sapere (originally "to taste, to perceive"), but the strong forms — sais, sait, sait — show consonant loss that has erased the link to the infinitive on the surface.

Indicatif

Conditionnel and subjonctif

Imperative

The imperative is built on the subjunctive stem, not the present indicative — a peculiarity savoir shares with avoir, être, and vouloir.

• (tu) sache — Know! / Be aware!
• (nous) sachons — Let's know / Let's be aware
• (vous) sachez — Know! / Be advised!

Participes

• Participe passé: su (masculine singular). Agreement with a preceding direct object follows the regular rules — la réponse, je l'ai sue — but in practice savoir takes propositional complements (que clauses) far more often than direct objects, so agreement rarely surfaces.
• Participe présent: sachant

Notes on the paradigm

Three things to memorize:

1. The strong/weak alternation in the present: strong sai- in je sais, tu sais, il sait; weak sav- in nous savons, vous savez, ils savent. Unlike pouvoir and devoir, savoir has only a two-way split — the third-person plural ils savent uses the same sav- stem as nous and vous, not a separate stem. This makes the present slightly easier to learn than its modal cousins.

2. The futur and conditionnel stem saur-: je saurai, tu sauras, il saura, nous saurons, vous saurez, ils sauront. The same stem powers je saurais, tu saurais. Like pouvoir's pourr-, the saur- stem has no obvious relationship to the infinitive — you just memorize it. Note: saurai (futur) and saurais (conditionnel) differ only by a final -s, identical in pronunciation in most accents.

3. The subjunctive stem sach-: que je sache, que tu saches, qu'il sache. This stem also feeds the imperative (sache, sachons, sachez) and the participe présent (sachant). You'll meet sache very early — in the fixed expressions que je sache ("as far as I know") and pas que je sache ("not that I know of") — long before you formally study the subjunctive.

Use 1: Knowing a fact

The bare-direct-object construction — savoir + a noun — names knowledge of a specific piece of information. The object is typically a fact, a date, a number, an answer.

This usage overlaps with English know the answer, know the time, know the code, and the structure is identical: savoir + direct object. The crucial constraint comes when comparing to connaître — see below — but the bare je sais [fact] form is unambiguous.

Use 2: Knowing that — savoir + que

When the object is a whole proposition rather than a single fact, French uses savoir que + indicative. The clause that follows expresses something the speaker considers true.

The que clause stays in the indicative because the speaker presents the information as factual. This is the default for savoir que in affirmative sentences and is one of the cleanest cases of indicative-after-clause-verb in French.

The negation puzzle: je ne sais pas si vs je ne sais pas que

When savoir is negated, English speakers expect the subjunctive (because the speaker doesn't claim the fact is true). French is more conservative: it keeps the indicative, but the conjunction shifts.

• Je ne sais pas que
  • indicative
  is rare and presupposes the embedded clause is true (je ne savais pas qu'il était médecin — "I didn't know he was a doctor," with qu'il était médecin presented as factual).
• Je ne sais pas si
  • indicative
  is the everyday "I don't know whether/if X."

The si clause — French equivalent of English embedded whether — always takes the indicative after savoir, never the subjunctive. This is one of the points where French is more indicative-friendly than learners expect.

Use 3: Knowing how to — the modal use

This is savoir in its modal incarnation: savoir + bare infinitive = "to know how to / can." Like every modal, savoir sits next to the infinitive without a preposition, and the meaning of the whole is "have the learned skill of doing X."

The English translation can is misleading — French je peux nager is grammatical but means something else (current physical or circumstantial ability, see below). For a learned skill that the subject has internalized — swimming, reading, driving, playing an instrument, speaking a language, cooking — French uses savoir. This is non-negotiable; switching to pouvoir changes the meaning.

Languages: savoir parler vs parler

A common subtlety: to talk about speaking a language as a skill you possess, French uses either savoir parler or simply parler. The bare parler le français is the everyday way to say "I speak French as part of my skill set"; savoir parler le français emphasizes the learned competence.

Both are acceptable; the bare parler is more common in self-introduction.

Use 4: Polite and idiomatic uses

The fixed que je sache / pas que je sache

These two formulas are constant fillers in spoken French. The sache is subjunctive, but no learner thinks about that — they're treated as units.

The negative form pas que je sache is one of the most common short answers in French conversation. Its structure is technically (je ne pense) pas que je sache — but only the tail survives in everyday use.

The set phrase faire savoir

Faire savoir = "let know / inform / make known." This is a causative construction (see faire + infinitive) used heavily in formal letters, emails, and announcements.

This is the formal correspondence equivalent of me dire — slightly more elevated, common in business email.

Sachez que — formal advisory

The imperative sachez que opens an advisory: "be advised that, please be aware that." It marks formal register and is common in announcements, signs, and official communication.

Savoir vs connaître — the make-or-break split

Both verbs translate as English know, but they cover different territories. The split is one of the most stable in French and worth drilling until automatic.

savoir is for information: facts, formulas, dates, codes, skills, propositions. Anything you can hold in your head as data, anything you've learned to do, anything you can express as "I know that..."

connaître is for familiarity: people, places, books, songs, fields, atmospheres. Anything you have direct acquaintance with, anything you can claim to recognize from experience.

The structural diagnostic is sharp:

• savoir can be followed by a que clause, an interrogative clause (où, quand, comment, si), or an infinitive (modal use). It can also take a direct object that is a piece of information.
• connaître is followed only by a direct object (a noun phrase). It cannot take a que clause, an interrogative clause, or an infinitive.

This rules out je connais que tu es là (impossible) and je connais nager (impossible). Whenever you're tempted to use connaître with anything other than a noun phrase, switch to savoir.

The borderline case: la réponse

Both je sais la réponse and je connais la réponse are heard, but they have different shadings:

• Je sais la réponse — I have the answer in my head as data. The standard, neutral version.
• Je connais la réponse — I'm familiar with the answer; I've encountered it before. Slightly less common, often suggests "I've seen this question before."

In quiz-show or test contexts, je sais la réponse is overwhelmingly the right choice.

Personal acquaintance — never savoir

This is the most stable rule in the system: people are always known with connaître, never savoir.

The same goes for places: je connais Lyon (I know Lyon, I've been there); je sais Lyon is impossible. Even though English speakers might say "I know Lyon" meaning "I've been there," in French this requires connaître.

For the full paradigm of connaître and the additional uses, see connaître.

Savoir in the imparfait vs passé composé

Like pouvoir and vouloir, savoir shows different meanings in the two main past tenses, and choosing well is one of the markers of fluency.

• Je savais
  • complement
  (imparfait) = "I knew" — the state of knowing existed in the past.
• J'ai su
  • complement
  (passé composé) = "I found out / I learned" — the moment of acquiring the knowledge.

The same logic applies to negation: je ne savais pas = "I didn't know" (state of not-knowing); je n'ai pas su = "I didn't find out / I never learned." The aspectual contrast is the only way French expresses what English splits across "knew" vs "found out."

Common Mistakes

Mistake 1: Using savoir for personal acquaintance.

Mistake 2: Using connaître with a clause or infinitive.

Mistake 3: Using pouvoir for a learned skill.

Mistake 4: Using the subjunctive after savoir que in negation.

Mistake 5: Confusing je sais and je connais with la chanson, le livre, etc.

Mistake 6: Saying Je sais le français for "I speak French."

Mistake 7: Forgetting that the imperative is built on the subjunctive stem.

Key takeaways

Savoir covers what English splits between "know" (facts) and "know how to" (skills). Memorize the two-way present alternation (sais/sait — savons/savez/savent), the futur/conditionnel stem saur-, and the unique subjunctive/imperative stem sach- that produces high-frequency forms like que je sache and sachez que. The past participle is su, regular in agreement.

The four uses are: knowing a fact (direct object), knowing that (savoir que + indicative), knowing how to (modal use, savoir + infinitive), and the polite/idiomatic uses (que je sache, sachez que, faire savoir). When negated, savoir que commonly switches to savoir si + indicative.

The hardest single point is the split with connaître: savoir for information, connaître for familiarity. People and places always take connaître; clauses and infinitives always take savoir. The aspectual contrast in the past — je savais (knew) vs j'ai su (found out) — works exactly like the equivalent contrast for pouvoir (was able vs managed to) and vouloir (wanted vs decided).