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 couldn't sub you couldn't sub he 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 he couldn't be subbing we couldn't be subbing you couldn't be subbing they couldn't be subbing
Perfect	V-ing perfect
I couldn't have subbed you couldn't have subbed he 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 he 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
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
couldn't I sub? couldn't you sub? couldn't he 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 he be subbing? couldn't we be subbing? couldn't you be subbing? couldn't they be subbing?
Perfect	V-ing perfect
couldn't I have subbed? couldn't you have subbed? couldn't he 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 he have been subbing? couldn't we have been subbing? couldn't you have been subbing? couldn't they have been subbing?