I could mix you could mix she could mix we could mix you could mix they could mix
V-ing form
I could be mixing you could be mixing she could be mixing we could be mixing you could be mixing they could be mixing
Perfect
I could have mixed you could have mixed she could have mixed we could have mixed you could have mixed they could have mixed
V-ing perfect
I could have been mixing you could have been mixing she could have been mixing we could have been mixing you could have been mixing they could have been mixing
Negation
Simple form
I couldn't mix you couldn't mix she couldn't mix we couldn't mix you couldn't mix they couldn't mix
V-ing form
I couldn't be mixing you couldn't be mixing she couldn't be mixing we couldn't be mixing you couldn't be mixing they couldn't be mixing
Perfect
I couldn't have mixed you couldn't have mixed she couldn't have mixed we couldn't have mixed you couldn't have mixed they couldn't have mixed
V-ing perfect
I couldn't have been mixing you couldn't have been mixing she couldn't have been mixing we couldn't have been mixing you couldn't have been mixing they couldn't have been mixing
Interrogative form
Simple form
could I mix? could you mix? could she mix? could we mix? could you mix? could they mix?
V-ing form
could I be mixing? could you be mixing? could she be mixing? could we be mixing? could you be mixing? could they be mixing?
Perfect
could I have mixed? could you have mixed? could she have mixed? could we have mixed? could you have mixed? could they have mixed?
V-ing perfect
could I have been mixing? could you have been mixing? could she have been mixing? could we have been mixing? could you have been mixing? could they have been mixing?
Interro-negative form
Simple form
couldn't I mix? couldn't you mix? couldn't she mix? couldn't we mix? couldn't you mix? couldn't they mix?
V-ing form
couldn't I be mixing? couldn't you be mixing? couldn't she be mixing? couldn't we be mixing? couldn't you be mixing? couldn't they be mixing?
Perfect
couldn't I have mixed? couldn't you have mixed? couldn't she have mixed? couldn't we have mixed? couldn't you have mixed? couldn't they have mixed?
V-ing perfect
couldn't I have been mixing? couldn't you have been mixing? couldn't she have been mixing? couldn't we have been mixing? couldn't you have been mixing? couldn't they have been mixing?