Answer:
I can tell you that René Descartes, the French philosopher and mathematician, argued in his philosophical treatise "Meditations on First Philosophy" that the distinction between waking life and dreams is not always clear, and that there is no sure test to determine whether one is dreaming or awake. He claimed that the experiences in a dream can seem just as real as those in waking life, and that it is only after waking up that one realizes it was a dream.
In terms of identifying that one is in a dream, there are certain dream signs that can indicate that one is dreaming, such as physical impossibilities, repetitive events or actions, and a distorted sense of time. However, these signs are not foolproof and can be difficult to recognize in the moment, especially if the dream feels real.
In summary, Descartes' argument is that there is no sure way to determine whether one is dreaming or awake, and that the experiences in a dream can be just as vivid and convincing as those in waking life.