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