a menos que
conjunctionCEFR B1
What does “a menos que” mean in English?
unless
unless (a menos que + subjunctive — always; most common everyday form)
Example sentences
No podremos proceder con la firma del contrato a menos que el abogado revise las cláusulas primero.
We won't be able to proceed with signing the contract unless the lawyer reviews the clauses first.
Llegaremos a tiempo a menos que haya un atasco en la circunvalación; suele estar colapsada los lunes.
We'll arrive on time unless there's a traffic jam on the ring road; it tends to be congested on Mondays.
El proyecto se entregará dentro del plazo a menos que surjan imprevistos técnicos graves.
The project will be delivered within the deadline unless serious technical issues arise.
How to use it
A menos que means 'unless' and always triggers subjunctive. It is the most common translation for 'unless' in everyday Spanish, slightly more colloquial than a no ser que. 'No podremos terminar a menos que el cliente apruebe el presupuesto' — the entire main proposition (not finishing) is contingent on the exception not occurring. The negative force in English ('unless') is built into the conjunction — the main clause does not need additional negation unless the meaning calls for it.
Common mistake
A menos que always takes subjunctive. Like a no ser que, the 'unless' meaning is fully encoded in the conjunction — do not add a negative particle to the embedded clause: *'a menos que no haya' changes the meaning (it would then mean 'as long as there isn't', not 'unless there is'). A menos que is interchangeable with a no ser que; choose based on register preference.