I could estimate you could estimate she could estimate we could estimate you could estimate they could estimate
V-ing form
I could be estimating you could be estimating she could be estimating we could be estimating you could be estimating they could be estimating
Perfect
I could have estimated you could have estimated she 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 she could have been estimating we could have been estimating you could have been estimating they could have been estimating
Negation
Simple form
I could not estimate you could not estimate she could not estimate we could not estimate you could not estimate they could not estimate
V-ing form
I could not be estimating you could not be estimating she could not be estimating we could not be estimating you could not be estimating they could not be estimating
Perfect
I could not have estimated you could not have estimated she could not have estimated we could not have estimated you could not have estimated they could not have estimated
V-ing perfect
I could not have been estimating you could not have been estimating she could not have been estimating we could not have been estimating you could not have been estimating they could not have been estimating
Interrogative form
Simple form
could I estimate? could you estimate? could she estimate? could we estimate? could you estimate? could they estimate?
V-ing form
could I be estimating? could you be estimating? could she be estimating? could we be estimating? could you be estimating? could they be estimating?
Perfect
could I have estimated? could you have estimated? could she 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 she have been estimating? could we have been estimating? could you have been estimating? could they have been estimating?
Interro-negative form
Simple form
could I not estimate? could you not estimate? could she not estimate? could we not estimate? could you not estimate? could they not estimate?
V-ing form
could I not be estimating? could you not be estimating? could she not be estimating? could we not be estimating? could you not be estimating? could they not be estimating?
Perfect
could I not have estimated? could you not have estimated? could she not have estimated? could we not have estimated? could you not have estimated? could they not have estimated?
V-ing perfect
could I not have been estimating? could you not have been estimating? could she not have been estimating? could we not have been estimating? could you not have been estimating? could they not have been estimating?