I could concern you could concern he could concern we could concern you could concern they could concern
V-ing form
I could be concerning you could be concerning he could be concerning we could be concerning you could be concerning they could be concerning
Perfect
I could have concerned you could have concerned he could have concerned we could have concerned you could have concerned they could have concerned
V-ing perfect
I could have been concerning you could have been concerning he could have been concerning we could have been concerning you could have been concerning they could have been concerning
Negation
Simple form
I could not concern you could not concern he could not concern we could not concern you could not concern they could not concern
V-ing form
I could not be concerning you could not be concerning he could not be concerning we could not be concerning you could not be concerning they could not be concerning
Perfect
I could not have concerned you could not have concerned he could not have concerned we could not have concerned you could not have concerned they could not have concerned
V-ing perfect
I could not have been concerning you could not have been concerning he could not have been concerning we could not have been concerning you could not have been concerning they could not have been concerning
Interrogative form
Simple form
could I concern? could you concern? could he concern? could we concern? could you concern? could they concern?
V-ing form
could I be concerning? could you be concerning? could he be concerning? could we be concerning? could you be concerning? could they be concerning?
Perfect
could I have concerned? could you have concerned? could he have concerned? could we have concerned? could you have concerned? could they have concerned?
V-ing perfect
could I have been concerning? could you have been concerning? could he have been concerning? could we have been concerning? could you have been concerning? could they have been concerning?
Interro-negative form
Simple form
could I not concern? could you not concern? could he not concern? could we not concern? could you not concern? could they not concern?
V-ing form
could I not be concerning? could you not be concerning? could he not be concerning? could we not be concerning? could you not be concerning? could they not be concerning?
Perfect
could I not have concerned? could you not have concerned? could he not have concerned? could we not have concerned? could you not have concerned? could they not have concerned?
V-ing perfect
could I not have been concerning? could you not have been concerning? could he not have been concerning? could we not have been concerning? could you not have been concerning? could they not have been concerning?