English verb conjugation
COULD VARY

Regular verb: vary - varied - varied

Affirmation

Simple form	V-ing form
I could vary you could vary he could vary we could vary you could vary they could vary	I could be varying you could be varying he could be varying we could be varying you could be varying they could be varying
Perfect	V-ing perfect
I could have varied you could have varied he could have varied we could have varied you could have varied they could have varied	I could have been varying you could have been varying he could have been varying we could have been varying you could have been varying they could have been varying

Negation

Simple form	V-ing form
I couldn't vary you couldn't vary he couldn't vary we couldn't vary you couldn't vary they couldn't vary	I couldn't be varying you couldn't be varying he couldn't be varying we couldn't be varying you couldn't be varying they couldn't be varying
Perfect	V-ing perfect
I couldn't have varied you couldn't have varied he couldn't have varied we couldn't have varied you couldn't have varied they couldn't have varied	I couldn't have been varying you couldn't have been varying he couldn't have been varying we couldn't have been varying you couldn't have been varying they couldn't have been varying

Interrogative form

Simple form	V-ing form
could I vary? could you vary? could he vary? could we vary? could you vary? could they vary?	could I be varying? could you be varying? could he be varying? could we be varying? could you be varying? could they be varying?
Perfect	V-ing perfect
could I have varied? could you have varied? could he have varied? could we have varied? could you have varied? could they have varied?	could I have been varying? could you have been varying? could he have been varying? could we have been varying? could you have been varying? could they have been varying?

Interro-negative form

Simple form	V-ing form
couldn't I vary? couldn't you vary? couldn't he vary? couldn't we vary? couldn't you vary? couldn't they vary?	couldn't I be varying? couldn't you be varying? couldn't he be varying? couldn't we be varying? couldn't you be varying? couldn't they be varying?
Perfect	V-ing perfect
couldn't I have varied? couldn't you have varied? couldn't he have varied? couldn't we have varied? couldn't you have varied? couldn't they have varied?	couldn't I have been varying? couldn't you have been varying? couldn't he have been varying? couldn't we have been varying? couldn't you have been varying? couldn't they have been varying?