One can organize nature in a hierarchy, starting from elementary particles and ending with consciousness. At each level some properties apply, but at the immediately higher level some other properties apply. For example, electrons have mass and spin, but electricity has potential and intensity. Chemical compounds have density and conductivity, whereas biological organisms have growth and reproduction. At each level a new set of properties "emerge". Supervenience takes it for granted that nature works this way, but offers no explanation at why at a higher level we would find electricity instead of, say, huicity or flowixity (imaginary properties): why and how just does properties? Why and how the mind emerges from the brain? Ultimately, this is the dilemma of "mental causation": how does the brain cause the mind? In general, this is the dilemma of "second-order properties": how do properties at one level cause properties at another level?

Kim does not have final answers but illustrates the strategic moves that contemporary philosophers make when faced with these dilemmas.