I could study you could study she could study we could study you could study they could study
Forma con V-ing
I could be studying you could be studying she could be studying we could be studying you could be studying they could be studying
Perfecto
I could have studied you could have studied she could have studied we could have studied you could have studied they could have studied
Perfecto con V-ing
I could have been studying you could have been studying she could have been studying we could have been studying you could have been studying they could have been studying
Negación
Forma simple
I could not study you could not study she could not study we could not study you could not study they could not study
Forma con V-ing
I could not be studying you could not be studying she could not be studying we could not be studying you could not be studying they could not be studying
Perfecto
I could not have studied you could not have studied she could not have studied we could not have studied you could not have studied they could not have studied
Perfecto con V-ing
I could not have been studying you could not have been studying she 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 she study? could we study? could you study? could they study?
Forma con V-ing
could I be studying? could you be studying? could she be studying? could we be studying? could you be studying? could they be studying?
Perfecto
could I have studied? could you have studied? could she have studied? could we have studied? could you have studied? could they have studied?
Perfecto con V-ing
could I have been studying? could you have been studying? could she have been studying? could we have been studying? could you have been studying? could they have been studying?
Forma interro-negativa
Forma simple
could I not study? could you not study? could she not study? could we not study? could you not study? could they not study?
Forma con V-ing
could I not be studying? could you not be studying? could she not be studying? could we not be studying? could you not be studying? could they not be studying?
Perfecto
could I not have studied? could you not have studied? could she not have studied? could we not have studied? could you not have studied? could they not have studied?
Perfecto con V-ing
could I not have been studying? could you not have been studying? could she not have been studying? could we not have been studying? could you not have been studying? could they not have been studying?