Quick answer: Forget means to fail to remember to take or do something. Leave (something somewhere) means to go away without taking something — whether remembered or not. “I forgot my keys” emphasises the memory failure. “I left my keys at home” states the location. Crucially, you must say where when using leave. For a fuller definition, see the Cambridge Dictionary entry for ‘forget’.
Comparison Table
| Word | Focus | Location needed? | Example |
|---|---|---|---|
| forget | failure of memory | no | I forgot my phone. |
| leave | physical location of object | yes | I left my phone at the office. |
Understanding Forget
Forget describes a mental process — you did not remember to bring something, do something, or think of something. The focus is on the person’s mental state. You can forget without saying where the object is. Forget can be followed by a noun, an infinitive, or a gerund (with different meanings).
I forgot my umbrella again.
She forgot to call him.
Don’t forget your passport!
I’ll never forget visiting Paris for the first time.
Forget + infinitive vs forget + gerund
“I forgot to lock the door” means I did not lock it (I failed to do so). “I forgot locking the door” means I did lock it but cannot remember doing so. The infinitive form is far more common.
Understanding Leave
Leave (something) describes the physical position of an object — you went somewhere without the object. Importantly, when using leave in this sense, you must say where the object is: “I left my bag at the restaurant.” You cannot say “I left my bag” alone to mean you forgot to bring it.
I left my wallet in the car.
She left her coat on the train.
He left his phone at home on purpose.
I must have left my keys at the office.
Common Mistakes
✗ I left my umbrella. (incomplete — left it where?)
✓ I left my umbrella at the restaurant. or I forgot my umbrella.
✗ I forgot my glasses at the cinema. (grammatically possible but unusual; leave is more natural here)
✓ I left my glasses at the cinema.
✗ I forgot turning off the oven. (implies you turned it off but can’t remember)
✓ I forgot to turn off the oven. (you didn’t turn it off)
Also compare: Remember vs Remind, Lose vs Miss, Bring vs Take. Browse all confusing word pairs →
Quick Check: Forget or Leave?
Four questions — choose the correct word.
1. “I ___ my phone on the bus.” (giving location)
2. “Don’t ___ to bring your passport tomorrow!”
3. “She ___ her keys at home again.”
4. “I completely ___ his birthday!” (memory failure)
Frequently Asked Questions
What is the difference between forget and leave?
Forget focuses on the mental failure to remember. Leave (something somewhere) states the physical location of an object you went without. You must specify where when using leave in this sense.
Can I say “I forgot my keys at home”?
It is used informally in some dialects, but in standard British English it is unusual to say where when using forget. Native speakers would more naturally say “I left my keys at home” (location) or “I forgot my keys” (no location).
Do I always need to give a location with leave?
Yes, when using leave to mean you went away without something. “I left my bag” alone is unclear or sounds like you abandoned it permanently. You must say: “I left my bag at the hotel.”
What is the past tense of forget?
The past tense is forgot and the past participle is forgotten: “I forgot my keys” / “I have forgotten where I put them.” The past tense of leave is left: “I left my keys at home.”
What is the difference between “forget to do” and “forget doing”?
“Forget to do” means you did not do it: “I forgot to lock the door.” “Forget doing” means you did it but cannot recall it: “I have no memory of signing that form — I must have forgotten signing it.”
Can leave mean deliberately not taking something?
Yes. “She left her phone at home on purpose.” Leave is neutral about whether the action was intentional. Forget always implies unintentional failure.
Is “I forgot my bag at the office” correct?
In American English this construction is sometimes heard, but in British English it is non-standard. The preferred British forms are “I forgot my bag” (no location) or “I left my bag at the office” (with location).
Can leave be followed by an infinitive?
In the sense of “leaving something behind,” no. But leave has other uses: “She left me waiting for an hour” (left + object + present participle) means she went away and I had to wait.
How do I say I forgot to do something in the future?
Use forget with a to-infinitive: “Don’t forget to call her.” / “I must not forget to post the letter.” You cannot use leave for failing to remember to do an action.
What is the noun form of forget?
There is no standard everyday noun directly from forget. You would say “I have a terrible memory” or describe the experience: “It was a moment of forgetfulness.” Forgetful is the related adjective.