Forms
Basecan
Negativecannot
Contractedcan't
Past formcould
Past negativecould not
Past contractedcouldn't
Question patternCan I / you / he …?
Meanings & usage
- Ability: “She can speak three languages.” Present mental or physical capability
- Permission: “Can I borrow your pen?” Informal, conversational
- Possibility: “It can get cold at night.” General possibility, not specific
- Request: “Can you help me?” Informal request
- Offer: “I can give you a ride.” Volunteering to help
Tense patterns
How this modal combines with a base verb across time references. The modal itself doesn’t conjugate; the time meaning comes from what you attach.
Reference
Affirmative
Negative
Question
Present
I can work
I can't work
Can I work?
Past (ability)
I could work
I couldn't work
Could I work?
Perfect (speculation)
She can't have left already
She can't have gone
Can she have finished?
Continuous
I can be working from home
I can't be working late
Can I be working there?
Common mistakes
Use may instead of can in formal writing when asking permission ("May I leave?" vs "Can I leave?").
Don't double modals: can be able to is wrong — pick one.