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