unless

unless — conjunction

1. Introduces a condition that must NOT happen for the main statement to be possibl

1.conjunctionB1
Definition

Introduces a condition that must NOT happen for the main statement to be possible — the main part of the sentence holds true in every situation except when this condition exists.

Example

Élise will not go to the beach tomorrow unless the storm has passed by morning.

not…unless + present perfect

Unless a major earthquake destroys the building, the family reunion will happen on Sunday.

Unless + clause at start of sentence

Common collocations
  • not…unless
  • never…unless
  • unless otherwise
  • unless + present tense
Synonyms
  • if not

    The most common alternative; 'unless' is preferred when stating the only exception rather than a general condition

  • except when

    More formal and less frequent; places heavier emphasis on the exceptional nature of the condition

Antonyms
  • if

    Presents the condition that makes something happen; 'unless' presents the condition that stops something from happening

Grammar Patterns

unless + clause (present tense)

Usage Note

The verb in the unless-clause takes the present tense even when the meaning refers to the future. Unlike 'if not', 'unless' emphasises the one situation that would prevent the main action from happening.

Common Mistakes

Unless he will call, we will cancel the order.
Unless he calls, we will cancel the order.
Use present tense, not 'will', after 'unless' when referring to the future.
Unless if it rains, the match will go ahead.
Unless it rains, the match will go ahead.
Do not use 'if' after 'unless'; the two words together are redundant.

unless — preposition

Synonym discussion

Sense: conjunction/1

'Unless' and 'if not' overlap heavily, but 'unless' highlights the sole condition that would block the main statement — 'I'll go unless it rains' focuses on rain as the only obstacle, while 'I'll go if it doesn't rain' presents a neutral condition. 'Except when' is more formal and often used for habitual exceptions ('The shop is open at 10 am except when the manager is late'). 'Otherwise' works differently: it refers back to a previously stated condition rather than introducing a new one ('Leave now; otherwise you will miss the bus'). For most everyday exceptions, 'unless' is the most natural choice.

if not ↗except whenotherwise ↗

Common collocations

Phrases

  • not…unless
  • never…unless
  • unless otherwise

Etymology

Middle EnglishOld EnglishModern English

Unless comes from the medieval phrase 'on less than', which meant 'on a smaller condition than (what one might expect)'. People in the 13th century used it to say that something would happen on an easier or less demanding condition. Over the next two hundred years, 'on less than' was compressed first to 'onlesse' and then to 'unless', and the meaning shifted from 'a lesser condition' to the modern sense of 'except if'.