Explain the doctrine of eternal return.
This is going to be difficult. The doctrine of eternal return essentially configures time in a cyclical pattern and not a linear one. In this light, the life we lead, we end up leading repeatedly. If time and space are indeed infinite, then the implication here would be that there would invariably be repeating patterns to existence and consciousness. This means that we, as human beings, are not necessarily living a life that is completely and absolutely authentic. Rather, figments and fragments of it have been repeated as part of a vast time/ space cosmology. This notion is something that is a part of Hinduism, but with a direction towards the advancement of the spirit. Nietzsche really honed in on eternal return in his work. From an intellectual standpoint, he argued that eternal return means that all ideas are borne out of something else. There can really not be something as a "pure" thought or something that has not come from something else. In the idea of consciousness, the challenge is understanding that we, as human beings, are part of a cyclical pattern of life of being in the world and part of this is repeating. Eternal return is a concept that Nietzsche feels adds weight to our existence, pinning us down and making us recognize an "unbearable burden." If you are interested in a literary exploration of this, consider Kundera's The Unbearable Lightness of Being.