Warning, this verb may not exist. Conjugation is given as example.
Affirmation
Simple form
I could keen keen you could keen keen he could keen keen we could keen keen you could keen keen they could keen keen
V-ing form
I could be keen keening you could be keen keening he could be keen keening we could be keen keening you could be keen keening they could be keen keening
Perfect
I could have keen keened you could have keen keened he could have keen keened we could have keen keened you could have keen keened they could have keen keened
V-ing perfect
I could have been keen keening you could have been keen keening he could have been keen keening we could have been keen keening you could have been keen keening they could have been keen keening
Negation
Simple form
I could not keen keen you could not keen keen he could not keen keen we could not keen keen you could not keen keen they could not keen keen
V-ing form
I could not be keen keening you could not be keen keening he could not be keen keening we could not be keen keening you could not be keen keening they could not be keen keening
Perfect
I could not have keen keened you could not have keen keened he could not have keen keened we could not have keen keened you could not have keen keened they could not have keen keened
V-ing perfect
I could not have been keen keening you could not have been keen keening he could not have been keen keening we could not have been keen keening you could not have been keen keening they could not have been keen keening
Interrogative form
Simple form
could I keen keen? could you keen keen? could he keen keen? could we keen keen? could you keen keen? could they keen keen?
V-ing form
could I be keen keening? could you be keen keening? could he be keen keening? could we be keen keening? could you be keen keening? could they be keen keening?
Perfect
could I have keen keened? could you have keen keened? could he have keen keened? could we have keen keened? could you have keen keened? could they have keen keened?
V-ing perfect
could I have been keen keening? could you have been keen keening? could he have been keen keening? could we have been keen keening? could you have been keen keening? could they have been keen keening?
Interro-negative form
Simple form
could I not keen keen? could you not keen keen? could he not keen keen? could we not keen keen? could you not keen keen? could they not keen keen?
V-ing form
could I not be keen keening? could you not be keen keening? could he not be keen keening? could we not be keen keening? could you not be keen keening? could they not be keen keening?
Perfect
could I not have keen keened? could you not have keen keened? could he not have keen keened? could we not have keen keened? could you not have keen keened? could they not have keen keened?
V-ing perfect
could I not have been keen keening? could you not have been keen keening? could he not have been keen keening? could we not have been keen keening? could you not have been keen keening? could they not have been keen keening?