English verb conjugation
COULD MODIFY

Regular verb: modify - modified - modified

Affirmation

Simple form	V-ing form
I could modify you could modify he could modify we could modify you could modify they could modify	I could be modifying you could be modifying he could be modifying we could be modifying you could be modifying they could be modifying
Perfect	V-ing perfect
I could have modified you could have modified he could have modified we could have modified you could have modified they could have modified	I could have been modifying you could have been modifying he could have been modifying we could have been modifying you could have been modifying they could have been modifying

Negation

Simple form	V-ing form
I couldn't modify you couldn't modify he couldn't modify we couldn't modify you couldn't modify they couldn't modify	I couldn't be modifying you couldn't be modifying he couldn't be modifying we couldn't be modifying you couldn't be modifying they couldn't be modifying
Perfect	V-ing perfect
I couldn't have modified you couldn't have modified he couldn't have modified we couldn't have modified you couldn't have modified they couldn't have modified	I couldn't have been modifying you couldn't have been modifying he couldn't have been modifying we couldn't have been modifying you couldn't have been modifying they couldn't have been modifying

Interrogative form

Simple form	V-ing form
could I modify? could you modify? could he modify? could we modify? could you modify? could they modify?	could I be modifying? could you be modifying? could he be modifying? could we be modifying? could you be modifying? could they be modifying?
Perfect	V-ing perfect
could I have modified? could you have modified? could he have modified? could we have modified? could you have modified? could they have modified?	could I have been modifying? could you have been modifying? could he have been modifying? could we have been modifying? could you have been modifying? could they have been modifying?

Interro-negative form

Simple form	V-ing form
couldn't I modify? couldn't you modify? couldn't he modify? couldn't we modify? couldn't you modify? couldn't they modify?	couldn't I be modifying? couldn't you be modifying? couldn't he be modifying? couldn't we be modifying? couldn't you be modifying? couldn't they be modifying?
Perfect	V-ing perfect
couldn't I have modified? couldn't you have modified? couldn't he have modified? couldn't we have modified? couldn't you have modified? couldn't they have modified?	couldn't I have been modifying? couldn't you have been modifying? couldn't he have been modifying? couldn't we have been modifying? couldn't you have been modifying? couldn't they have been modifying?