I could staple you could staple he could staple we could staple you could staple they could staple
V-ing form
I could be stapling you could be stapling he could be stapling we could be stapling you could be stapling they could be stapling
Perfect
I could have stapled you could have stapled he could have stapled we could have stapled you could have stapled they could have stapled
V-ing perfect
I could have been stapling you could have been stapling he could have been stapling we could have been stapling you could have been stapling they could have been stapling
Negation
Simple form
I couldn't staple you couldn't staple he couldn't staple we couldn't staple you couldn't staple they couldn't staple
V-ing form
I couldn't be stapling you couldn't be stapling he couldn't be stapling we couldn't be stapling you couldn't be stapling they couldn't be stapling
Perfect
I couldn't have stapled you couldn't have stapled he couldn't have stapled we couldn't have stapled you couldn't have stapled they couldn't have stapled
V-ing perfect
I couldn't have been stapling you couldn't have been stapling he couldn't have been stapling we couldn't have been stapling you couldn't have been stapling they couldn't have been stapling
Interrogative form
Simple form
could I staple? could you staple? could he staple? could we staple? could you staple? could they staple?
V-ing form
could I be stapling? could you be stapling? could he be stapling? could we be stapling? could you be stapling? could they be stapling?
Perfect
could I have stapled? could you have stapled? could he have stapled? could we have stapled? could you have stapled? could they have stapled?
V-ing perfect
could I have been stapling? could you have been stapling? could he have been stapling? could we have been stapling? could you have been stapling? could they have been stapling?
Interro-negative form
Simple form
couldn't I staple? couldn't you staple? couldn't he staple? couldn't we staple? couldn't you staple? couldn't they staple?
V-ing form
couldn't I be stapling? couldn't you be stapling? couldn't he be stapling? couldn't we be stapling? couldn't you be stapling? couldn't they be stapling?
Perfect
couldn't I have stapled? couldn't you have stapled? couldn't he have stapled? couldn't we have stapled? couldn't you have stapled? couldn't they have stapled?
V-ing perfect
couldn't I have been stapling? couldn't you have been stapling? couldn't he have been stapling? couldn't we have been stapling? couldn't you have been stapling? couldn't they have been stapling?