I can travel you can travel he can travel we can travel you can travel they can travel
V-ing form
I can be travelling you can be travelling he can be travelling we can be travelling you can be travelling they can be travelling
Perfect
I can have travelled you can have travelled he can have travelled we can have travelled you can have travelled they can have travelled
V-ing perfect
I can have been travelling you can have been travelling he can have been travelling we can have been travelling you can have been travelling they can have been travelling
Negation
Simple form
I cannot travel you cannot travel he cannot travel we cannot travel you cannot travel they cannot travel
V-ing form
I cannot be travelling you cannot be travelling he cannot be travelling we cannot be travelling you cannot be travelling they cannot be travelling
Perfect
I cannot have travelled you cannot have travelled he cannot have travelled we cannot have travelled you cannot have travelled they cannot have travelled
V-ing perfect
I cannot have been travelling you cannot have been travelling he cannot have been travelling we cannot have been travelling you cannot have been travelling they cannot have been travelling
Interrogative form
Simple form
can I travel? can you travel? can he travel? can we travel? can you travel? can they travel?
V-ing form
can I be travelling? can you be travelling? can he be travelling? can we be travelling? can you be travelling? can they be travelling?
Perfect
can I have travelled? can you have travelled? can he have travelled? can we have travelled? can you have travelled? can they have travelled?
V-ing perfect
can I have been travelling? can you have been travelling? can he have been travelling? can we have been travelling? can you have been travelling? can they have been travelling?
Interro-negative form
Simple form
can I not travel? can you not travel? can he not travel? can we not travel? can you not travel? can they not travel?
V-ing form
can I not be travelling? can you not be travelling? can he not be travelling? can we not be travelling? can you not be travelling? can they not be travelling?
Perfect
can I not have travelled? can you not have travelled? can he not have travelled? can we not have travelled? can you not have travelled? can they not have travelled?
V-ing perfect
can I not have been travelling? can you not have been travelling? can he not have been travelling? can we not have been travelling? can you not have been travelling? can they not have been travelling?