English verb conjugation
COULD SUB

Regular verb: sub - subbed - subbed

Affirmation

Simple form	V-ing form
I could sub you could sub he could sub we could sub you could sub they could sub	I could be subbing you could be subbing he could be subbing we could be subbing you could be subbing they could be subbing
Perfect	V-ing perfect
I could have subbed you could have subbed he 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 he 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
I could not sub you could not sub he could not sub we could not sub you could not sub they could not sub	I could not be subbing you could not be subbing he could not be subbing we could not be subbing you could not be subbing they could not be subbing
Perfect	V-ing perfect
I could not have subbed you could not have subbed he could not have subbed we could not have subbed you could not have subbed they could not have subbed	I could not have been subbing you could not have been subbing he could not have been subbing we could not have been subbing you could not have been subbing they could not have been subbing

Interrogative form

Simple form	V-ing form
could I sub? could you sub? could he sub? could we sub? could you sub? could they sub?	could I be subbing? could you be subbing? could he be subbing? could we be subbing? could you be subbing? could they be subbing?
Perfect	V-ing perfect
could I have subbed? could you have subbed? could he 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 he 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
could I not sub? could you not sub? could he not sub? could we not sub? could you not sub? could they not sub?	could I not be subbing? could you not be subbing? could he not be subbing? could we not be subbing? could you not be subbing? could they not be subbing?
Perfect	V-ing perfect
could I not have subbed? could you not have subbed? could he not have subbed? could we not have subbed? could you not have subbed? could they not have subbed?	could I not have been subbing? could you not have been subbing? could he not have been subbing? could we not have been subbing? could you not have been subbing? could they not have been subbing?