Antti Revonsuothat “they have no life of their own; causally speaking, they are not something “over and above” neuro-
biological processes” (Searle 2004: 113). It is, claims Searle, a fact established by an overwhelming
amount of evidence that all of our conscious states are caused by brain processes. Recognizing
this fact, and the other theses of BN, amounts to a solution (or a dissolution) of the traditional
mind-body problem in philosophy, claims Searle. It is the duty of the biological sciences and
the neurosciences to take over and figure out exactly how the causal mechanisms between brain
processes and consciousness work. The philosophers should just get out of the way.
3 Critical Remarks about Biological NaturalismIt is however not immediately obvious whether the core ideas of BN amount to an internally
coherent explanation. How is it possible to simultaneously hold the two claims: “consciousness
is causally reducible to the brain” and “consciousness is ontologically subjective; therefore, con-
sciousness is not ontologically reducible to the brain”? Searle explicitly does hold them: “You
can do a causal reduction of consciousness to its neuronal substrate, but that reduction does
not lead to an ontological reduction because consciousness has a first-person ontology” (Searle
2004: 123).
Searle tries to explain the difference between causal and ontological reduction. By causal
reduction Searle means that, causally speaking, consciousness owes its existence to the underly-
ing lower-level brain processes that causally bring it about. Although neuroscience doesn’t have
it yet figured out, there is a full causal, neurophysiological explanation as to where, when, and
how conscious states are causally brought about in the brain; so far, we just lack the details of
that explanation.
Searle appears to accept the two main components of the supervenience relationship between
consciousness and the brain (although he is somewhat reluctant to use the concept of superveni-
ence): there can be no difference in conscious states without a corresponding difference in the
underlying brain states (the covariance principle), and the conscious states owe their existence
to the underlying brain states (the principle of ontological dependency). He also accepts that
BN represents emergentism:
If we define emergent properties of a system of elements as properties which can be
explained by the behavior of the individual elements, but which are not properties of
elements construed individually, then it is a trivial consequence of my view that mental
properties are emergent properties of neurophysiological systems.
(Searle 1987: 228)What, then, is the “ontological subjectivity” or “first-person ontology” that escapes ontologi-
cal reduction, and why does it escape it? Searle explains it along the following lines. Objective
physical phenomena that can be ontologically reduced to their causal base have two types
of properties, surface properties (how they appear to human observers) and underlying causal
properties (how they “really” are, independent of human observation). Causal reduction leads
to ontological reduction in the case of third-person objective phenomena (such as the physi-
cal explanation of visible light) because we get rid of the surface properties (how visible light
looks like to us in our conscious perception), as they are not really properties of the physical
phenomenon at all, but of our observations, mere appearances. But in the case of consciousness,
consciousness is identical to its appearance; its appearance is identical with the subjective ontology
of consciousness. The appearance of consciousness is its essential feature; and a thing cannot be
deprived of its essential features while still preserving the same ontology. Thus, the appearance