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