could vary
Regular verb: vary - varied- varied

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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	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 	
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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	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 	Perfect 	V-ing perfect 	
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? 	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 	Perfect 	V-ing perfect 	
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? 	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?