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 could not vary you could not vary he could not vary we could not vary you could not vary they could not vary	I could not be varying you could not be varying he could not be varying we could not be varying you could not be varying they could not be varying
Perfect	V-ing perfect
I could not have varied you could not have varied he could not have varied we could not have varied you could not have varied they could not have varied	I could not have been varying you could not have been varying he could not have been varying we could not have been varying you could not have been varying they could not 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
could I not vary? could you not vary? could he not vary? could we not vary? could you not vary? could they not vary?	could I not be varying? could you not be varying? could he not be varying? could we not be varying? could you not be varying? could they not be varying?
Perfect	V-ing perfect
could I not have varied? could you not have varied? could he not have varied? could we not have varied? could you not have varied? could they not have varied?	could I not have been varying? could you not have been varying? could he not have been varying? could we not have been varying? could you not have been varying? could they not have been varying?