John Searle proposes a theory of mind which he calls "biological naturalism": that consciousness arises naturally from the brain. He argues that consciousness is neither a separate entity nor an illusion. "...both dualism and materialism are trying to say something true but because of the philosophical tradition they end up saying something false. Which part is false and which true? Dualism says truly that consciousness is a real feature of the real world and is neither eliminable nor reducible to something else. But it says falsely that consciousness is not an ordinary part of the physical world we all live in, but it inhabits a separate metaphysical realm. Materialism says truly that the universe consists entirely of physical particles in fields of force (or whatever the ultimately true physical theory says are the basic building blocks of the universe) but it says falsely that consciousness as an irreducible, subjective, qualitative mental phenomenon does not exist." (Biological Naturalism, 2004).

David Chalmers (Absent Qualia, Fading Qualia, Dancing Qualia,1995), contra Searle, puts forward a much wider view of what kind of physical substrate can underlie consciousness. Chalmers speculates that pipes and people, organised in the right way, would be conscious. A set of water pipes can no more constitute a conscious entity than they can form a nuclear reactor core. This is because water pipes don't have the necessary functional (or, as Searle would say, causal) capability: of being like neurons or fissile material respectively. Unlike the case of the nuclear reactor, however, the necessary and sufficient properties for consciousness have yet to be determined though this camp does not believe that just ANY functional equivalence will suffice.

It may be the case that the electrical activity of neurons is their relevant property. If so then analogue silicon chips that perform the same electrical functions could be substitued for neurons and so form a device just like the brain, consciousness included. The important point here is that it is not sufficient just to have the same functional organisation as imagined by Chalmers: neither water pipes nor people could form a conscious functional organization however you arrange them because they don't have the necessary electrical properties. Note that this failing also applies to computer chips: computational functionalism is insufficient (see, for example, Searle's Chinese Room argument).