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