Personal is an adjective meaning private or belonging to one individual — "please don't read my personal emails". Personnel is a noun meaning the people employed by an organisation — "only authorised personnel may enter". They also sound different: PER-son-al puts the stress at the front, per-son-NEL at the end.
Different parts of speech entirely
Personal modifies a noun. It marks something as private, individual, or done in person: personal data, a personal favour, personal experience, a personal appearance. It never names a group of people.
Personnel names people — specifically, the workforce of a company, army, hospital or department. It behaves as a collective noun and normally takes a plural verb: "personnel are being redeployed", not "personnel is". It also names the department that manages staff, though most organisations now call that Human Resources.
Each in use
- "She keeps her personal life off social media."
- "This is a personal matter and I'd rather not discuss it here."
- "All medical personnel must complete the training by Friday."
- "The base lost thirty personnel to the reorganisation."
The test
Try substituting staff or employees. If the sentence still works — "all medical staff must complete the training" — you want personnel. If instead you can substitute private or individual, you want personal.
A spelling cue: personnel is the one with the double n, and it is stressed at the end — per-son-NEL. Personal has a single n and the stress at the front — PER-son-al. Say the word aloud and the spelling follows.
The mistakes that show up most
The commonest is a sign or job title reading "Human Resources Personal" or "Personal Department", which turns a staffing office into something oddly intimate. The reverse error — "my personnel opinion" — appears in emails and reads as a typo.
Two further points. Personnel has no plural form: never write personnels. And because it is collective, you cannot say a personnel; the singular is a member of staff or an employee.
As for personal, it does appear as a noun in one narrow sense: the personals, meaning small ads placed by individuals. There is also personable, meaning pleasant and easy to get on with, which is a separate word again and not a synonym for either.
