There are well known objections to type-type identity (IEP) such as multiple realization and Kripke's argument, but I don't know any objections acceptable (by the majority of philosophers) to this identity version of physicalism. Are there any serious problems in identifying a particular mental event with some physical event?

  • 4
    Since token identity is currently the primary version of physicalism objections against it largely overlap with objections to physicalism generally. I do not think there are any that most philosophers consider conclusive, but some prominent ones are arguments from qualia, see SEP, and arguments from mismatch between physical and mental properties, see e.g. argument for the mind-body dualism from immateriality of thoughts.
    – Conifold
    Feb 26 at 10:42
  • Thanks a lot, yeah, I was thinking about qualia but it is a challenge rather than an objection. Thanks for the references.
    – Arian
    Feb 26 at 11:46
  • 1
    Voting to close because the question uses technical jargon with no attempt to explain it. Feb 26 at 23:46
  • Is there a Nobel Prize for philosophy? Mar 6 at 15:38
  • @AgentSmith Nope!
    – J D
    Mar 7 at 21:15

2 Answers 2


Identity Theory is a claim that the brain state is identical to the conscious state: https://iep.utm.edu/identity/ Philosophers have treated Identity Theory AS a theory, and tried to falsify it. There are a variety of problems with it that have been identified:

  1. Multiple Realizability. We experience a thought over time, say 2+2=4. Over that time, we have synaptic connections dissolve, and new ones forming, repeatedly. We also have continually varying patterns of energy activation passing thru our brains. Neither the network, nor the activation pattern, remain constant, despite the constant thought. This though therefore CANNOT be identical to either a brain network structure, nor an activation pattern. We are also able to communicate this thought to others, despite their different neural structure, and activation patterns.

  2. Identity of Indiscernibles: Qualia are not indiscernible from brain states. Identity Theory fails the basic criteria of identity.

Physicalism has adopted several different strategies to address these failed falsification tests. The most common is Functionalism. Functionalism ALSO is an Identity Theory, but what is claimed to be identical to consciousness is a function. In my example, the function of 2+2=4 is asserted to be identical to the awareness of 2+2=4.

In Functionalism, functions ALSO have an identity to brain states, but that identity is the token-token identity your question references. Many brain states are postulated that can produce slightly different 2+2=4 functions. HOWEVER, the brain is postulated to act BASED on functions. Somehow, the brain is aware of the large suite of tokens that can produce the related 2+2=4 functions, and keeps its status within that suite. So functionalism postulates that the Functional family resemblance is what is causally effective in bounding the states the brain enters. Token identity itself is casually irrelevant, and cannot EXPLAIN anything. The family of functions are asserted to the type-type identical to consciousness, and therefore this type-identity is the explanation of consciousness.

Objections to functionalism:

  1. The primary objection is the other side of the coin to multiple realizability, it is a surplus of functions relative to consciousness. One can write 2+2=4, design an and gate structure that executes 2+2=4, write a digital code that executes 2+2=4, design a neural net that generates 2+2=4, etc. Yet, 99.999% of these functions will not be conscious. Functionalism is not a sufficient condition for consciousness. INCLUDING IN OUR BRAINS! We process 2+2=4 in many cases UNCONSCIOUSLY -- hence even the family of related 2+2=4 CANNOT BE IDENTICAL TO CONSCIOUSNESS.

  2. Our brains don't actually DO functions! We humans developed the concept of functions from introspection on how we do analysis. We then created digital computers to do this sort of stepwise analytic processing. BUT -- when we examine our neurology, we are wired COMPLETELY DIFFERENTLY than our digital computers, even though our digital computers were structured on how we think we think. Our brains are wired with as associative neural nets, which are analog, not digital. Functions are not discernable at all in our wiring. Daniel Dennett postulates that we run a "virtual" digital computer on our analog neural net structure. Interestingly, much recent work in Artificial Intelligence involves running virtual neural net processing on the actual digital wiring structure of digital computers. BUT back to Functionalism -- if we don't have physical functions in our neurology, yet we are conscious, then functions cannot be a physical explanation of consciousness.

These objections have generated a variety of proposals to get around them.

Paul Churchland proposed that the operation of a recursive neural net IS consciousness -- in an effort to revive neural identity theory. This proposal falls afoul of the first objection to functionalism -- our brains do recursive neural net processing all the time, for basically everything, yet consciousness is a rarity.

Higher Order Processing, and Global Workspace Theory, and Strange Loops, were all proposals to limit the TYPE of functions that could be identical to consciousness. the problem for each is that we have instantaneous conscious qualia that is not higher order, global, etc., AND we have higher order processing, globally shared info, etc. that are not conscious. These narrower functions do not match the experiences of consciousness in functional objection 1, AND do not address functional objection 2 at all.

Integrated Information theory is a proposal that Functional Identify requires, additionally, that the substrate the function is run on must have a high wiring uniqueness (high Phi) in order to generate consciousness (or that the consciousness generated is proportional to Phi). IIT runs afoul of both objections to functionalism -- we don't run functions, and most of our processing is completely unconscious despite being run on either high or moderate Phi wiring.

These various failures to make Identity Theories work, are why most physicalists today DON'T hold by an Identity Theory, and instead are emergentists. Emergent physicalism holds that some neural structures, or possibly some types of neural processing, lead to consciousness emerging. In emergent physicalism consciousness is not IDENTICAL, but a CONSEQUENCE of brains.

I hope this discussion of Identity Theory has made clear the problem with token Identity. Theories of consciousness seek to explain why we are conscious, and for physicalist theories, how the brain maintains our being conscious. Token Identity removes any predictive power from Identity theory, making it an untestable claim, with no predictive or explanatory utility. If Token Identity is all one has, there is no way for a brain to maintain consciousness or functional stability, and neither our functional behavior, nor our conscious awareness are explainable. And in particular, their stability and apparent effectiveness over time is counter-predicted.

In Popperian philosophy of science terms, the token-token claim is an effort to maintain a dogmatic assertion of Mind/Brain identity, while vitiating it of any testable consequences, due to every actual predictive consequence of an actual Identity Theory being refuted.

  • Thank you for your detailed review on some physical theories. Although I am agree with you that token theory is not predictive and has not explanatory utility, but some version of it such as anomalous monism is not so ad hoc. Consciousness is a challenge for any version of physicalism but as a real objection?(I don't think so)
    – Arian
    Mar 6 at 9:06
  • @Arian. An ontology which cannot encompass any of our observed data (all observations are experiences) — is about as decisive an objection as one can find. Anomalous monism asserts conscious emergence, and two way causation. It is basically emergent dualism. The one thing added to try to paper over that it isn’t monism is deliberately untestable. “Supervenience” is explicitly NOT “identity” and is a deliberately vague and undefined relationship to evade the falsifications that actual predictive identity claims fail. It is a similar evasion tactic to avoid test ability like token-token is.
    – Dcleve
    Mar 12 at 4:40

Your question, as I read it, seems straight forward:

Are there any serious problems in identifying a particular mental event with some physical event?

I think there plenty of philosophical objections to identifying mental events with physical events IF one ignores naturalistic epistemology. That being said, if one embraces it, then one clearly has to accept neuroimaging as the nail in the coffin of any philosophical theory that attempts to refute the general equivalence between mental and physical events. Neural correlates of consciousness are simply too irrefutable to deny statements like "physical events in the brain are strongly correlated to mental events".

I think some philosophers have an axe to grind, as Conifold noted, with some operating principles of physicalism, particlarly those who want to validate some non-empirical transcendental reality. In this case, if one were to accept that NCCs fundamentally show an obdurate metaphysical relationship (of any kind), it becomes much more difficult to allow metaphysical presupposition that posit additional realities. For instance, the need for a soul is obviated by NCCs since they're both non-empirical (to orthodox formulations of empiricism that reject paranormality) and non-parsimonious.

Beyond the powerful correlation, however, all is fair in love, war, and metaphysics. In no way do NCCs endorse particular views in regards to shed light on mental causation, or weigh in on the spectrum of positions from subjective idealism to eliminative materialism, other than to suggest that one can claim that there are no known instances of mental events without the appropriate physical events that we have come to know in love that underlie thinking. That is, clearly the affecting the brain affects the functioning of mental events. And then that fact is free to be used strategically.

  • As your link notes, Francis Crick played a key role in recruiting a generation of researchers into the neurologic search for consciousness, and the presumption of finding the "neural correlates of consciousness" has been that field's goal for 3 decades. However, the output of that search has been far LESS than the goal -- the "correlates" identified in your Wikipedia link are entirely to pre-conscious processing. Citing that search as having been successful, rather than its basically total failure, is a misrepresentation of the state of the science.
    – Dcleve
    Mar 10 at 16:14
  • @lol I had to include non-orthodox empiricism in my response just to stave off justifiable metaphysical commentary on your part. Apparently, I should have put more thought in to other parts. Let's see. I made no claim that NCCs have been successful in a scientific sense of establishing a science of consciousness. I think the granularity in neuroimaging simply won't allow for it. My claim is that NCCs are evidence that a philosopher cannot ignore when considering the metaphysical necessity of physical events as a basis for mental events...
    – J D
    Mar 10 at 16:43
  • thus, identity theory, in some formulation, is the only way of associating mental events with physical events (according to empirical orthodoxy), and that there are no real philosophical problems doing so. That the state of science is lacking isn't an objection, because scientific methodology has the purpose of starting with epistemic and ontic simplicity and creating a reliable theory from it.
    – J D
    Mar 10 at 16:45
  • I consider the success of neurologic research in characterizing the neurologic basis of pre-conscious processing, to be explicit evidence against functional identity theory. The data from correlations between brain damage and loss of conscious mental faculties is strong evidence against the "radio receiver" idealist and dualist model. The failure to actually correlate to consciousness, however, and the adoption of homunculus models that track the "entry into consciousness" by many researchers, support the basic dualist model of "interface of brain to consciousness", not Crick's reductionism.
    – Dcleve
    Mar 10 at 16:52
  • In my review of The Myth of an Afterlife, I agree that the data from cognition losses due to brain damage or chemical influence show that simple dualist models need to be adapted. I offered a model for how this data can be accommodated dualistically. I don't think it can be accommodated by idealism. See this review: amazon.com/gp/customer-reviews/R10Z02T2ZEYPFY/… To make materialism work as an alternative model, you would need to embrace strong emergence. IE Identity of consciousness with a physically emergent phenomenon.
    – Dcleve
    Mar 10 at 17:02

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