English verb conjugation
COULD SUB

Regular verb: sub - subbed - subbed

Affirmation

Simple form	V-ing form
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
Perfect	V-ing perfect
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
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
Perfect	V-ing perfect
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
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?
Perfect	V-ing perfect
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
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?
Perfect	V-ing perfect
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?