could discover
Regular verb: discover - discovered- discovered

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could discover
you could discover
she could discover
we could discover
you could discover
they could discover 	I could be discovering
you could be discovering
she could be discovering
we could be discovering
you could be discovering
they could be discovering	I could have discovered
you could have discovered
she could have discovered
we could have discovered
you could have discovered
they could have discovered	I could have been discovering
you could have been discovering
she could have been discovering
we could have been discovering
you could have been discovering
they could have been discovering	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't discover
you couldn't discover
she couldn't discover
we couldn't discover
you couldn't discover
they couldn't discover 	I couldn't be discovering
you couldn't be discovering
she couldn't be discovering
we couldn't be discovering
you couldn't be discovering
they couldn't be discovering	I couldn't have discovered
you couldn't have discovered
she couldn't have discovered
we couldn't have discovered
you couldn't have discovered
they couldn't have discovered	I couldn't have been discovering
you couldn't have been discovering
she couldn't have been discovering
we couldn't have been discovering
you couldn't have been discovering
they couldn't have been discovering	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I discover?
could you discover?
could she discover?
could we discover?
could you discover?
could they discover? 	could I be discovering?
could you be discovering?
could she be discovering?
could we be discovering?
could you be discovering?
could they be discovering? 	could I have discovered?
could you have discovered?
could she have discovered?
could we have discovered?
could you have discovered?
could they have discovered? 	could I have been discovering?
could you have been discovering?
could she have been discovering?
could we have been discovering?
could you have been discovering?
could they have been discovering? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I discover?
couldn't you discover?
couldn't she discover?
couldn't we discover?
couldn't you discover?
couldn't they discover? 	couldn't I be discovering?
couldn't you be discovering?
couldn't she be discovering?
couldn't we be discovering?
couldn't you be discovering?
couldn't they be discovering? 	couldn't I have discovered?
couldn't you have discovered?
couldn't she have discovered?
couldn't we have discovered?
couldn't you have discovered?
couldn't they have discovered? 	couldn't I have been discovering?
couldn't you have been discovering?
couldn't she have been discovering?
couldn't we have been discovering?
couldn't you have been discovering?
couldn't they have been discovering?