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