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