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 couldn't study you couldn't study she couldn't study we couldn't study you couldn't study they couldn't study
Forma con V-ing
I couldn't be studying you couldn't be studying she couldn't be studying we couldn't be studying you couldn't be studying they couldn't be studying
Perfecto
I couldn't have studied you couldn't have studied she couldn't have studied we couldn't have studied you couldn't have studied they couldn't have studied
Perfecto con V-ing
I couldn't have been studying you couldn't have been studying she couldn't have been studying we couldn't have been studying you couldn't have been studying they couldn't 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
couldn't I study? couldn't you study? couldn't she study? couldn't we study? couldn't you study? couldn't they study?
Forma con V-ing
couldn't I be studying? couldn't you be studying? couldn't she be studying? couldn't we be studying? couldn't you be studying? couldn't they be studying?
Perfecto
couldn't I have studied? couldn't you have studied? couldn't she have studied? couldn't we have studied? couldn't you have studied? couldn't they have studied?
Perfecto con V-ing
couldn't I have been studying? couldn't you have been studying? couldn't she have been studying? couldn't we have been studying? couldn't you have been studying? couldn't they have been studying?