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