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