According to most simple explanations, the demonstrative 이 can be used to talk about real physical things close to the speaker, 그 for things nearer the listener, and 저 things far from both.
But 이 can also be used in a more abstract sense, e.g. 이 달 – 'this month', and so can 그 , e.g. 그와 같은 경우에는 – 'in a case like that'.
Can 저 ever used for abstract things, or is it always used for real objects? Would the thing indicated always have to be visible?