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