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