English verb conjugation
COULD PREVENT

Regular verb: prevent - prevented - prevented

Affirmation

Simple form	V-ing form
I could prevent you could prevent he could prevent we could prevent you could prevent they could prevent	I could be preventing you could be preventing he could be preventing we could be preventing you could be preventing they could be preventing
Perfect	V-ing perfect
I could have prevented you could have prevented he could have prevented we could have prevented you could have prevented they could have prevented	I could have been preventing you could have been preventing he could have been preventing we could have been preventing you could have been preventing they could have been preventing

Negation

Simple form	V-ing form
I couldn't prevent you couldn't prevent he couldn't prevent we couldn't prevent you couldn't prevent they couldn't prevent	I couldn't be preventing you couldn't be preventing he couldn't be preventing we couldn't be preventing you couldn't be preventing they couldn't be preventing
Perfect	V-ing perfect
I couldn't have prevented you couldn't have prevented he couldn't have prevented we couldn't have prevented you couldn't have prevented they couldn't have prevented	I couldn't have been preventing you couldn't have been preventing he couldn't have been preventing we couldn't have been preventing you couldn't have been preventing they couldn't have been preventing

Interrogative form

Simple form	V-ing form
could I prevent? could you prevent? could he prevent? could we prevent? could you prevent? could they prevent?	could I be preventing? could you be preventing? could he be preventing? could we be preventing? could you be preventing? could they be preventing?
Perfect	V-ing perfect
could I have prevented? could you have prevented? could he have prevented? could we have prevented? could you have prevented? could they have prevented?	could I have been preventing? could you have been preventing? could he have been preventing? could we have been preventing? could you have been preventing? could they have been preventing?

Interro-negative form

Simple form	V-ing form
couldn't I prevent? couldn't you prevent? couldn't he prevent? couldn't we prevent? couldn't you prevent? couldn't they prevent?	couldn't I be preventing? couldn't you be preventing? couldn't he be preventing? couldn't we be preventing? couldn't you be preventing? couldn't they be preventing?
Perfect	V-ing perfect
couldn't I have prevented? couldn't you have prevented? couldn't he have prevented? couldn't we have prevented? couldn't you have prevented? couldn't they have prevented?	couldn't I have been preventing? couldn't you have been preventing? couldn't he have been preventing? couldn't we have been preventing? couldn't you have been preventing? couldn't they have been preventing?