I could execute you could execute she could execute we could execute you could execute they could execute
V-ing form
I could be executing you could be executing she could be executing we could be executing you could be executing they could be executing
Perfect
I could have executed you could have executed she could have executed we could have executed you could have executed they could have executed
V-ing perfect
I could have been executing you could have been executing she could have been executing we could have been executing you could have been executing they could have been executing
Negation
Simple form
I couldn't execute you couldn't execute she couldn't execute we couldn't execute you couldn't execute they couldn't execute
V-ing form
I couldn't be executing you couldn't be executing she couldn't be executing we couldn't be executing you couldn't be executing they couldn't be executing
Perfect
I couldn't have executed you couldn't have executed she couldn't have executed we couldn't have executed you couldn't have executed they couldn't have executed
V-ing perfect
I couldn't have been executing you couldn't have been executing she couldn't have been executing we couldn't have been executing you couldn't have been executing they couldn't have been executing
Interrogative form
Simple form
could I execute? could you execute? could she execute? could we execute? could you execute? could they execute?
V-ing form
could I be executing? could you be executing? could she be executing? could we be executing? could you be executing? could they be executing?
Perfect
could I have executed? could you have executed? could she have executed? could we have executed? could you have executed? could they have executed?
V-ing perfect
could I have been executing? could you have been executing? could she have been executing? could we have been executing? could you have been executing? could they have been executing?
Interro-negative form
Simple form
couldn't I execute? couldn't you execute? couldn't she execute? couldn't we execute? couldn't you execute? couldn't they execute?
V-ing form
couldn't I be executing? couldn't you be executing? couldn't she be executing? couldn't we be executing? couldn't you be executing? couldn't they be executing?
Perfect
couldn't I have executed? couldn't you have executed? couldn't she have executed? couldn't we have executed? couldn't you have executed? couldn't they have executed?
V-ing perfect
couldn't I have been executing? couldn't you have been executing? couldn't she have been executing? couldn't we have been executing? couldn't you have been executing? couldn't they have been executing?