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