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