English verb conjugation
COULD DEMONSTRATE

Regular verb: demonstrate - demonstrated - demonstrated

Affirmation

Simple form	V-ing form
I could demonstrate you could demonstrate he could demonstrate we could demonstrate you could demonstrate they could demonstrate	I could be demonstrating you could be demonstrating he could be demonstrating we could be demonstrating you could be demonstrating they could be demonstrating
Perfect	V-ing perfect
I could have demonstrated you could have demonstrated he could have demonstrated we could have demonstrated you could have demonstrated they could have demonstrated	I could have been demonstrating you could have been demonstrating he could have been demonstrating we could have been demonstrating you could have been demonstrating they could have been demonstrating

Negation

Simple form	V-ing form
I couldn't demonstrate you couldn't demonstrate he couldn't demonstrate we couldn't demonstrate you couldn't demonstrate they couldn't demonstrate	I couldn't be demonstrating you couldn't be demonstrating he couldn't be demonstrating we couldn't be demonstrating you couldn't be demonstrating they couldn't be demonstrating
Perfect	V-ing perfect
I couldn't have demonstrated you couldn't have demonstrated he couldn't have demonstrated we couldn't have demonstrated you couldn't have demonstrated they couldn't have demonstrated	I couldn't have been demonstrating you couldn't have been demonstrating he couldn't have been demonstrating we couldn't have been demonstrating you couldn't have been demonstrating they couldn't have been demonstrating

Interrogative form

Simple form	V-ing form
could I demonstrate? could you demonstrate? could he demonstrate? could we demonstrate? could you demonstrate? could they demonstrate?	could I be demonstrating? could you be demonstrating? could he be demonstrating? could we be demonstrating? could you be demonstrating? could they be demonstrating?
Perfect	V-ing perfect
could I have demonstrated? could you have demonstrated? could he have demonstrated? could we have demonstrated? could you have demonstrated? could they have demonstrated?	could I have been demonstrating? could you have been demonstrating? could he have been demonstrating? could we have been demonstrating? could you have been demonstrating? could they have been demonstrating?

Interro-negative form

Simple form	V-ing form
couldn't I demonstrate? couldn't you demonstrate? couldn't he demonstrate? couldn't we demonstrate? couldn't you demonstrate? couldn't they demonstrate?	couldn't I be demonstrating? couldn't you be demonstrating? couldn't he be demonstrating? couldn't we be demonstrating? couldn't you be demonstrating? couldn't they be demonstrating?
Perfect	V-ing perfect
couldn't I have demonstrated? couldn't you have demonstrated? couldn't he have demonstrated? couldn't we have demonstrated? couldn't you have demonstrated? couldn't they have demonstrated?	couldn't I have been demonstrating? couldn't you have been demonstrating? couldn't he have been demonstrating? couldn't we have been demonstrating? couldn't you have been demonstrating? couldn't they have been demonstrating?