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The Missing Concept That Could Unite Mind and Brain | Thomas Nagel
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Mind-brain identity theory faces a challenge from Kripke's modal argument, suggesting subjective experience and brain states are distinct because we can imagine one without the other—but Nagel proposes a deeper, unified concept might bridge this gap.
Key Insights
Mind-brain identity theory emerged in the mid-1950s as a materialist response to behaviorism, attempting to explain subjective experiences like pain by directly equating them with brain states.
Saul Kripke's modal argument, using distinctions between necessary and contingent, and analytic and synthetic, posits that scientific identities (like water is H2O) are necessarily true, yet subjective experiences (like pain) appear contingently linked to brain states (C-fibers), thus challenging identity theory.
Nagel argues that our inability to conceive of pain without C-fiber firing, or vice-versa, is due to distinct modes of conception: imagining from the 'inside' (subjective experience) versus describing from the 'outside' (neurological basis).
Nagel suggests a more fundamental, unifying concept might exist that necessarily entails both the external, material description of a brain state and the internal, subjective feeling of an experience, thus reconciling the apparent contingency.
The debate around mind-brain identity has fundamentally expanded theories of mind since the 1950s, stimulating research into functionalism, causal behaviorism, and significantly increasing interest in consciousness as the most challenging aspect of the mind-body problem.
The rise of mind-brain identity theory from behaviorism
Mind-brain identity theory, which posits that mental states are literally identical to physical brain states, gained traction in the mid-1950s as a successor to behaviorism. Behaviorism, influenced by Gilbert Ryle's 'The Concept of Mind,' analyzed mental language in terms of observable criteria and dispositions. However, philosophers like U.T. Place and J.J.C. Smart argued that this behavioral analysis failed to capture the essence of sensory experiences, such as feeling pain or tasting chocolate. They proposed that these internal subjective states should be identified not with external behaviors, but with specific internal brain states that occur concurrently with these experiences. A key aspect of this early theory was the assertion that this identity was contingent, meaning that the apparent ability to conceive of pain without a particular brain state, or vice versa, was not a genuine counterexample to the identity.
Kripke's challenge to mind-brain identity
Saul Kripke's influential 1970 paper introduced a significant challenge to mind-brain identity theory through his modal argument. Kripke distinguished between necessary and contingent truths, and analytic versus synthetic propositions. He argued that scientific identities, such as 'water is H2O' or 'heat is molecular motion,' are necessarily true, even if discovered empirically. This means that in any possible world, water would always be H2O. Applying this to the mind-body problem, Kripke contended that if pain is identical to C-fiber firing (a specific brain state), then this identity must hold necessarily. However, Kripke argued that we can coherently imagine pain occurring without C-fiber firing, and C-fiber firing without pain, suggesting the link is merely contingent. Since such a contingency appears possible, it implies that pain and C-fiber firing cannot be identical.
Nagel's alternative interpretation of apparent contingency
Thomas Nagel offers a nuanced critique of Kripke's argument, suggesting that the apparent possibility of conceiving pain without C-fiber firing (or vice versa) arises from different modes of conception, rather than a lack of identity. Nagel distinguishes between conceiving something from the 'inside'—through direct subjective experience—and conceiving it from the 'outside'—through objective, scientific description. When we imagine pain without C-fiber firing, according to Nagel, we are actually imagining what it is like to be in a state that *appears* to be pain from the inside, while simultaneously describing its external neurological correlate. These are distinct conceptual tools applied to the same underlying reality. Therefore, even if a necessary connection exists between the subjective experience of pain and the objective state of C-fiber firing, our current conceptual framework allows for these two perspectives to seem separable, leading to the illusion of contingency.
The need for a new, unifying concept
Nagel posits that the mind-body problem, as highlighted by Kripke's challenge, points towards a conceptual gap. He suggests that the identity between mental states and brain states might be necessarily true, but we currently lack the concepts to grasp this necessity. This could be resolved by positing a more fundamental underlying reality or concept that necessarily entails both the external, material description of a brain state and the internal, subjective feeling of an experience. This foundational concept would not be a mere psychological-physical law connecting two separate realms, but rather something from which both the mental and physical aspects derive. Such a concept would inherently possess both an 'outside' material aspect and an 'inside' mental aspect, explaining why they are inseparable and necessarily linked.
Beyond reductionism and dualism
Nagel rejects both strict reductive materialism (which claims brain states are *simply* mental states, leaving no room for subjective experience) and non-materialist views (which posit a separate, non-physical substance for consciousness). He argues that stating 'a brain state *is* a mental state' is not an analytic truth. Instead, it implies that some brain states possess mental properties, and this requires explanation. The contemporary approach, exemplified by David Papineau, uses analogies like the 'morning star' and 'evening star' (both Venus) to argue that apparent contingency in mental states is due to our naming conventions, not a lack of identity. However, Nagel points out that we understand Venus comprehensively, unlike the underlying unified concept for pain and brain states, which remains speculative. This speculative nature underscores the ongoing search for a deeper explanation.
The legacy of mind-brain identity debate
The prolonged engagement with mind-brain identity theory, including its challenges and proposed solutions, has profoundly shaped contemporary philosophy of mind. It has spurred the development of diverse theories, including functionalism and causal behaviorism, which attempt to bridge the gap between the mental and physical. Furthermore, the debate has significantly amplified interest in consciousness itself, identifying it as the most intractable aspect of the mind-body problem. This enduring intellectual stimulus, originating from the mid-20th century, continues to drive research and philosophical inquiry into the nature of subjectivity, awareness, and the fundamental relationship between mind and brain.
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The mind-body identity theory posits that mental states are literally identical to physical states of the brain. It emerged in the mid-1950s as a response to behaviorism, seeking to integrate the mind into a materialist worldview.
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Mentioned in this video
Author of 'The Concept of Mind', who analyzed mental language in terms of observable criteria.
Proposes an approach to mind-body identity using the Morning Star/Evening Star analogy, suggesting that apparent independence of mental and physical states is due to naming conventions.
Co-authored a paper arguing that behavioral analysis is insufficient for sensory experiences, proposing internal states.
Co-authored a paper arguing that behavioral analysis is insufficient for sensory experiences, proposing internal states.
Philosopher who presented an argument against mind-body identity theory based on necessity and possibility, particularly concerning pain and C-fibers.
Used as an analogy by David Papineau to illustrate how two different names can refer to the same underlying entity (Venus), suggesting a similar relationship for mind-body identity.
Used as an example of a scientific identity (water is H2O) that is necessary, contrasting with the contingent identity proposed for mental states and brain states.
Used as an analogy by David Papineau to illustrate how two different names can refer to the same underlying entity (Venus), suggesting a similar relationship for mind-body identity.
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