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