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