Philosophers call this the hard problem of consciousness. It is the latest version of a classic problem in the philosophy of mind called the "mind-body problem." A related problem is the problem of "meaning" or "understanding" (which philosophers call "intentionality"): what is the connection between our "thoughts" and "what we are thinking about" (i.e. objects and situations out in the world)? A third issue is the problem of "experience" (or "phenomenology"): If two people see the same thing, do they have the same experience? Or are there things "inside their head" (called "qualia") that can be different from person to person?