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