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