I could study you could study he could study we could study you could study they could study
Forma com V-ing
I could be studying you could be studying he could be studying we could be studying you could be studying they could be studying
Perfeito
I could have studied you could have studied he could have studied we could have studied you could have studied they could have studied
Perfeito com V-ing
I could have been studying you could have been studying he could have been studying we could have been studying you could have been studying they could have been studying
Negação
Forma simple
I could not study you could not study he could not study we could not study you could not study they could not study
Forma com V-ing
I could not be studying you could not be studying he could not be studying we could not be studying you could not be studying they could not be studying
Perfeito
I could not have studied you could not have studied he could not have studied we could not have studied you could not have studied they could not have studied
Perfeito com V-ing
I could not have been studying you could not have been studying he could not have been studying we could not have been studying you could not have been studying they could not have been studying
Forma interrogativa
Forma simple
could I study? could you study? could he study? could we study? could you study? could they study?
Forma com V-ing
could I be studying? could you be studying? could he be studying? could we be studying? could you be studying? could they be studying?
Perfeito
could I have studied? could you have studied? could he have studied? could we have studied? could you have studied? could they have studied?
Perfeito com V-ing
could I have been studying? could you have been studying? could he have been studying? could we have been studying? could you have been studying? could they have been studying?
Forma interro-Negação
Forma simple
could I not study? could you not study? could he not study? could we not study? could you not study? could they not study?
Forma com V-ing
could I not be studying? could you not be studying? could he not be studying? could we not be studying? could you not be studying? could they not be studying?
Perfeito
could I not have studied? could you not have studied? could he not have studied? could we not have studied? could you not have studied? could they not have studied?
Perfeito com V-ing
could I not have been studying? could you not have been studying? could he not have been studying? could we not have been studying? could you not have been studying? could they not have been studying?