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