Biological Naturalism and Biological RealismBiological Naturalism and Biological Realism
BN starts from the facts that we know beyond any reasonable doubts. Searle says that BN
is just “scientifically sophisticated common sense” applied to consciousness (Searle 2007). So,
what are the facts about consciousness? Searle summarizes BN as a set of four theses (Searle
2004: 113):1 Realism: Consciousness is a real phenomenon in the real world. Consciousness really exists,
in its own right, in the physical world. Its existence cannot be denied. Any theory that
gets rid of consciousness by eliminating or reducing it to something else, rejects this realist
thesis about consciousness and therefore rejects the most undeniable fact we know about
consciousness.
2 Neurophysiological causation and sufficiency: Consciousness is entirely caused by lower-level
neurophysiological processes in the brain. The causally sufficient conditions for any con-
scious phenomenon are in the brain.
3 Neurophysiological realization: Consciousness is a higher-level feature of the brain system. It
exists at a level higher than the level of neurons or synapses; individual neurons cannot be
conscious.
4 Mental causation: Consciousness has causal powers. Our voluntary behaviors are causally
driven by our conscious mental states.In addition to these four fundamental theses, BN needs a definition and description of “con-
sciousness.” Searle’s definition of consciousness says that consciousness consists of one’s states of
awareness or sentience or feeling (Searle 2007). The definition also points to the conditions under
which the phenomenon is to be found in the world: “Conscious states are those states of aware-
ness, sentience, or feeling that begin in the morning when you wake from a dreamless sleep and
continue throughout the day until you fall asleep or otherwise become ‘unconscious’ (Dreams
are also a form of consciousness)” (Searle 2007: 326).
The three essential features of consciousness are (1) qualitative character or ‘what-it-feels-like,’
(2) ontological subjectivity, and (3) global unity. All conscious states are qualitative in the sense that
having them feels like something. Conscious states cannot exist without their qualitative character.
All conscious states are subjective in the sense that they exist only when experienced by a human
or animal subject, some “I” whose conscious experiences they are. The subjectivity of conscious-
ness is ontological, meaning that it is a special mode of existence that only conscious phenomena
possess. The ontological subjectivity of consciousness prevents the ontological reduction of con-
sciousness to any purely objective phenomena, such as neuronal firings. All momentary con-
scious phenomena are parts of a single unified conscious field. Although our consciousness involves
many kinds of qualitative experiences at any given moment – say the text I see on the computer
screen, the music I hear in the background, the fresh breeze of cold air I feel coming from the
window, and the softness of the carpet under my bare feet – all these qualitatively different con-
tents of consciousness are experienced as happening simultaneously within one unified field by
one subject of experience. In a nutshell, for Searle, consciousness is unified qualitative subjectivity.2 The Explanation of Consciousness According to Biological Naturalism
One and the same physical system can have different levels of description that are not competing
or distinct; they are simply different levels within a single unified causal system. In this com-
pletely non-mysterious way, also the brain has many different levels of description. Higher-level
properties of a system can be causally explained by the lower-level or the micro-properties of the
same system. Conscious states are thus causally reducible to neurobiological processes. Searle says