Biological Naturalism and Biological Realism4 Biological RealismI have presented Biological Realism in its full formulation in Revonsuo (2006) (and brief
summaries in Revonsuo 2010, 2015). The basic thesis of BR is that “Consciousness is a real,
natural, biological phenomenon.” As it is “real,” it exists in physical space and time, and it
cannot be eliminated away or reduced to anything else. It is a “natural,” not supernatural or
metaphysically outlandish phenomenon. It is a biological phenomenon, existing among other
biologically based phenomena. It follows that the task of explaining consciousness falls to the
biological sciences, especially cognitive neuroscience that has defined itself as “the biology of
the mind.”
Therefore, if there is going to be a unified science of consciousness, any such research pro-
gram must be anchored to the biological sciences. The explanatory framework of the biological
sciences is the proper framework in which the explanation of consciousness will be sought. By
contrast, in the philosophy of mind, the models of explanation are typically drawn from the basic
physical sciences. The reductive unity of the physical sciences and the Deductive-Nomological
(D-N) model of explanation are typically taken for granted as the paradigms of scientific expla-
nation. The D-N model assumes that all scientific explanations and theories should look like our
best theories in physics: mathematically expressed exact laws of nature that accurately predict
and explain the behavior of physical entities. Theories describing higher-level macroscopic enti-
ties (liquid water, ice) can be logically derived from and reduced back to the fundamental laws
in physics (first to theories describing H 2 O molecules, then to hydrogen and oxygen atoms, and
finally to microphysics and quantum physics).
But explanation in the biological sciences does not typically follow the reductive D-N
model, and there are only few exact, mathematically described explanatory laws in biology.
Recent work in the philosophy of neuroscience has come up with a different model of explana-
tion for the life sciences: the multilevel mechanistic model, or multilevel explanation (see Bechtel
and Richardson 1992; Craver 2007, 2016). According to this model, complex physical systems
such as biological organisms consist of multiple levels of organization. These levels are real, onto-
logical levels in nature. Different phenomena (such as synapses, neurons, neural networks, the
whole central nervous system) reside at different levels of complexity. Higher-level phenomena
are constituted by lower-level phenomena but not reducible to them, because the higher-level
phenomena have causal powers at their own level of organization that go beyond those of the
lower-level phenomena. A synapse or a single neuron does not have the same causal powers as
the whole central nervous system does.
All of the above applies to the explanation of complex biological phenomena in general.
According to BR, we now simply need to place consciousness into this framework of expla-
nation. In the multilevel framework, consciousness as a biological phenomenon constitutes a
higher level of neurophysiological or neuroelectrical organization in the brain. Consciousness
can thus be reconceptualized as the phenomenal level of organization in the brain. Next, the mul-
tilevel explanatory model of consciousness should be constructed.
In general, a multilevel mechanistic model first describes a phenomenon in detail at its own
level, and then explains it by specifying its micro-level constitution, its origin (or causal history),
and its functional roles (or causal powers) in the world. All this can be achieved by placing the
phenomenon into the center of a causal-mechanical network that has several different explana-
tory dimensions (see Figure 14.1). The full explanation of a phenomenon requires multiple
levels of description and three different directions of explanation.
First, the essential features of consciousness itself should be described accurately, at their own
level, so that we will have precisely identified what the target phenomenon (the explanandum)