could invalidate
Regular verb: invalidate - invalidated- invalidated

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could invalidate
you could invalidate
she could invalidate
we could invalidate
you could invalidate
they could invalidate 	I could be invalidating
you could be invalidating
she could be invalidating
we could be invalidating
you could be invalidating
they could be invalidating	I could have invalidated
you could have invalidated
she could have invalidated
we could have invalidated
you could have invalidated
they could have invalidated	I could have been invalidating
you could have been invalidating
she could have been invalidating
we could have been invalidating
you could have been invalidating
they could have been invalidating	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't invalidate
you couldn't invalidate
she couldn't invalidate
we couldn't invalidate
you couldn't invalidate
they couldn't invalidate 	I couldn't be invalidating
you couldn't be invalidating
she couldn't be invalidating
we couldn't be invalidating
you couldn't be invalidating
they couldn't be invalidating	I couldn't have invalidated
you couldn't have invalidated
she couldn't have invalidated
we couldn't have invalidated
you couldn't have invalidated
they couldn't have invalidated	I couldn't have been invalidating
you couldn't have been invalidating
she couldn't have been invalidating
we couldn't have been invalidating
you couldn't have been invalidating
they couldn't have been invalidating	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I invalidate?
could you invalidate?
could she invalidate?
could we invalidate?
could you invalidate?
could they invalidate? 	could I be invalidating?
could you be invalidating?
could she be invalidating?
could we be invalidating?
could you be invalidating?
could they be invalidating? 	could I have invalidated?
could you have invalidated?
could she have invalidated?
could we have invalidated?
could you have invalidated?
could they have invalidated? 	could I have been invalidating?
could you have been invalidating?
could she have been invalidating?
could we have been invalidating?
could you have been invalidating?
could they have been invalidating? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I invalidate?
couldn't you invalidate?
couldn't she invalidate?
couldn't we invalidate?
couldn't you invalidate?
couldn't they invalidate? 	couldn't I be invalidating?
couldn't you be invalidating?
couldn't she be invalidating?
couldn't we be invalidating?
couldn't you be invalidating?
couldn't they be invalidating? 	couldn't I have invalidated?
couldn't you have invalidated?
couldn't she have invalidated?
couldn't we have invalidated?
couldn't you have invalidated?
couldn't they have invalidated? 	couldn't I have been invalidating?
couldn't you have been invalidating?
couldn't she have been invalidating?
couldn't we have been invalidating?
couldn't you have been invalidating?
couldn't they have been invalidating?