En Masse vs. In Mass
The fixed English expression is “en masse,” meaning all together or in large numbers at the same time. Cambridge records the two-word French-derived form “en masse”; “in mass” is not the form of this idiom in the reviewed evidence.
For the idiom meaning “all together” or “in large numbers,” write “en masse”: “The staff resigned en masse.”
Key details
Choose the right form
| Form | Meaning | Decision |
|---|---|---|
| en masse | all together or in large numbers at the same time | Use for the fixed idiom. |
| in mass | ordinary words that can occur literally in other constructions | Do not use as a replacement spelling for the idiom. |
Quick tests
Substitution test
Could you replace the expression with “all together” or “as a group”?
If yes: Use “en masse.”
If no: If you literally mean “in mass,” write the ordinary phrase required by that separate context.
Caveat: The idiom is the French-derived two-word form “en masse.”
Examples
The staff resigned en masse.
The group acted together.
The staff resigned in mass.
Better: The staff resigned en masse.
For the idiom meaning “all together,” use “en masse.”
Further guidance
Boundary
The ordinary English words “in mass” can occur compositionally in other contexts, but they are not a replacement spelling for this idiom.
Correct Form
Cambridge lists “en masse” as the adverbial expression.
Meaning
Use it when a group acts together or appears in large numbers.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- En masse — English meaning (opens in a new tab)Cambridge University Press · Dictionary record for the fixed adverbial expression en masse