Can you talk about something that does not exist as a sum of real things? Example: A unicorn does not exist, but it is the sum of real things. Obviously the real world that we talk about exists. A purple cow is the sum of purple and cow, both are real. So... is there anything that we can talk about that does not exist as a sum of real things? I think not, because our brain ONLY receives information from our 5 senses, which means everything that goes into it is from the REAL world.