could sub
Regular verb: sub - subbed- subbed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could sub
you could sub
she could sub
we could sub
you could sub
they could sub 	I could be subbing
you could be subbing
she could be subbing
we could be subbing
you could be subbing
they could be subbing	I could have subbed
you could have subbed
she could have subbed
we could have subbed
you could have subbed
they could have subbed	I could have been subbing
you could have been subbing
she could have been subbing
we could have been subbing
you could have been subbing
they could have been subbing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't sub
you couldn't sub
she couldn't sub
we couldn't sub
you couldn't sub
they couldn't sub 	I couldn't be subbing
you couldn't be subbing
she couldn't be subbing
we couldn't be subbing
you couldn't be subbing
they couldn't be subbing	I couldn't have subbed
you couldn't have subbed
she couldn't have subbed
we couldn't have subbed
you couldn't have subbed
they couldn't have subbed	I couldn't have been subbing
you couldn't have been subbing
she couldn't have been subbing
we couldn't have been subbing
you couldn't have been subbing
they couldn't have been subbing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I sub?
could you sub?
could she sub?
could we sub?
could you sub?
could they sub? 	could I be subbing?
could you be subbing?
could she be subbing?
could we be subbing?
could you be subbing?
could they be subbing? 	could I have subbed?
could you have subbed?
could she have subbed?
could we have subbed?
could you have subbed?
could they have subbed? 	could I have been subbing?
could you have been subbing?
could she have been subbing?
could we have been subbing?
could you have been subbing?
could they have been subbing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I sub?
couldn't you sub?
couldn't she sub?
couldn't we sub?
couldn't you sub?
couldn't they sub? 	couldn't I be subbing?
couldn't you be subbing?
couldn't she be subbing?
couldn't we be subbing?
couldn't you be subbing?
couldn't they be subbing? 	couldn't I have subbed?
couldn't you have subbed?
couldn't she have subbed?
couldn't we have subbed?
couldn't you have subbed?
couldn't they have subbed? 	couldn't I have been subbing?
couldn't you have been subbing?
couldn't she have been subbing?
couldn't we have been subbing?
couldn't you have been subbing?
couldn't they have been subbing?