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