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