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