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