The English conjunction unless expresses a condition that prevents something from happening. In French, there is no exact one-word equivalent. It is typically translated using the conjunction à moins que, which requires the subjunctive mood. Other constructions are possible depending on formality, register, and clarity, including sauf si, excepté si, si ce n’est que, and restructured sentences using sinon or conditional phrases. The correct choice depends on the verb tense, sentence structure, and whether the clause is affirmative or negative.

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À moins que (+ subjunctive)

À moins que is the most direct and common translation of unless, especially in formal and written French. It always introduces a subordinate clause and is followed by a verb in the subjunctive.

• Je n’y vais pas, à moins qu’il ne m’invite.
  I’m not going unless he invites me.
• Elle partira, à moins que tu ne la retiennes.
  She will leave unless you hold her back.
• Nous annulerons, à moins qu’il ne fasse beau.
  We will cancel unless the weather is nice.

Note the ne explétif often used with à moins que, especially in formal French. It has no negative meaning and is optional in spoken language. The subjunctive is required regardless of whether the ne is used.

Use à moins que when:

• introducing a condition that would make the main clause false
• the clause includes a subject and conjugated verb
• formality or precision is required

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Sauf si / Excepté si (+ indicative)

Sauf si and excepté si both mean unless in the sense of except if. They are followed by the indicative mood and are used more frequently in spoken French than à moins que, especially when the sentence is simple or when the clause is affirmative.

• Je viens demain, sauf si je suis malade.
  I’m coming tomorrow unless I’m sick.
• Il réussira, sauf s’il abandonne.
  He’ll succeed unless he gives up.
• Tu peux sortir, excepté s’il pleut.
  You can go out unless it rains.

Use sauf si or excepté si when:

• the clause is factual and does not require the subjunctive
• the structure is simple
• the tone is conversational or informal

These forms are inappropriate in highly formal writing when a subjunctive-dependent structure is expected.

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Si ce n’est que

This is a literary or formal phrase meaning except that or unless. It often introduces an exception to what was just said, and not a direct conditional.

• Tout était parfait, si ce n’est que la fin était trop rapide.
  Everything was perfect, unless (except that) the ending was too quick.
• Il aurait réussi, si ce n’est qu’il a tout abandonné.
  He would have succeeded, unless (except that) he gave everything up.

This phrase is not a full substitute for unless in all contexts. It introduces a qualification or restriction on a previous statement, not a general conditional clause.

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Sinon

Sinon means otherwise and is often used to imply unless by restructuring the sentence. The idea is conditional, but expressed as a consequence instead of a subordinate clause.

• Dépêche-toi, sinon on va rater le train.
  Hurry up, unless we’ll miss the train. (literally: otherwise we’ll miss the train)
• Révise, sinon tu vas échouer.
  Study, unless you’ll fail.

This structure is informal and useful in spoken French. It avoids the need for subjunctive or complex clauses but is less precise.

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Restructuring with conditional phrases

Sometimes, instead of translating unless directly, French restructures the sentence with a si (if) clause or by making the condition explicit in a different way.

• Unless you help me, I won’t finish.
  → Si tu ne m’aides pas, je ne finirai pas.
  If you don’t help me, I won’t finish.
• You can’t enter unless you’re invited.
  → Tu ne peux pas entrer si tu n’es pas invité.
  You can’t enter if you’re not invited.

This is common in both written and spoken French, especially when clarity is preferred over formality. It avoids the need for subjunctive or ambiguous turns of phrase.

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Summary

• À moins que is the most direct translation of unless, and requires the subjunctive.
• Sauf si and excepté si are used with the indicative and are common in spoken French.
• Si ce n’est que introduces exceptions, mostly in formal or literary language.
• Sinon can restructure the sentence to imply unless as otherwise.
• Rewriting the sentence using si (if) clauses with negative verbs is often the clearest option.

Choice depends on register, verb mood, and whether the context is written, spoken, formal, or casual.