Welcome back. In our previous lesson, we grappled with the "hard problem" of consciousness, distinguishing it from the "easy problems" of cognitive function. We established that the core difficulty lies in the explanatory gap between the objective, physical processes of the brain and the subjective, first-person reality of experience. The central question—why does information processing feel like anything at all?—appears to resist the standard methods of scientific reduction.
Today, we will see how this conceptual challenge is weaponized into direct arguments against physicalism. We will move from defining the problem to analyzing two of the most influential thought experiments in modern philosophy of mind, both of which contend that the existence of phenomenal consciousness demonstrates that a purely physical account of the world is incomplete. We will dissect Thomas Nagel's argument about the nature of subjective facts and Frank Jackson's famous "knowledge argument."
1. Nagel and the Subjective Point of View
In 1974, the philosopher Thomas Nagel published a paper that profoundly shifted the debate, titled "What is it like to be a bat?". His central claim is that physicalism, in its ambition to create a purely objective account of reality, necessarily leaves out the most essential feature of consciousness: its subjective character.
Let's begin by defining this core concept.
What is it Like to be a Bat? - the hard problem of consciousness
The video "What is it Like to be a Bat?" by Jeffrey Kaplan offers a superb walkthrough of Nagel's argument. It begins by establishing the fundamental definition of consciousness that Nagel employs.
Please watch the segment from consciousness is 'what it's like'. Pay close attention to the thought experiments used to distinguish between entities that have conscious experiences (like a person) and those that don't (like a rock). The key takeaway is Nagel's definition: "An organism has conscious mental states if and only if there is something that it is like to be that organism." This "what-it's-likeness" is also referred to as phenomenal character, or qualia.
With this definition in hand, Nagel introduces his famous example. He chooses a bat not because it is simple, but because its primary mode of perceiving the world—echolocation—is so profoundly alien to our own. This makes the core of his argument particularly vivid.
What is it Like to be a Bat? - the hard problem of consciousness
Let's continue with the Kaplan video to understand why the bat is such a powerful example.
Watch the next part of the video, which explains the bat example and points of view. The crucial point is not that we can't imagine behaving like a bat (flying, shrieking), but that we cannot imagine what it is like for the bat to experience the world through sonar. This leads to Nagel's conclusion that facts about conscious experience "embody a particular point of view."
This brings us to the heart of Nagel's attack on physicalism. Your background in physics has trained you to seek explanations that are objective and observer-independent. The goal of a physical theory is to describe reality as it is, not merely how it appears to a specific type of observer. Nagel argues that while this method is perfect for explaining the external world, it fails for consciousness precisely because consciousness is a point of view.
Let's see how the argument comes together.
What is it Like to be a Bat? - the hard problem of consciousness
The final part of the argument contrasts the method of objective science with the nature of subjective experience.
Please watch the segment from Nagel's attack on physicalism. The video uses the analogy of lightning: science explains lightning by moving away from its subjective appearance (a bright flash) to its objective reality (electrical discharge). This works because the appearance and the reality are distinct. But with a conscious experience like pain, there is no distinction between its appearance and its reality. The "seeming" is the phenomenon. Therefore, any objective, physicalist theory that, by its nature, abstracts away from the subjective point of view will inevitably miss the essence of what it's trying to explain.
To fully appreciate the precision of Nagel's reasoning, there is no substitute for reading his original words.
[PDF] What is it like to be a bat
In this seminal paper, Nagel lays out the case that the subjective character of experience is the primary obstacle to a physicalist reduction of the mind.
Please read the following key passages: Begin with the second paragraph, "defining subjective character", where Nagel formally introduces the "what it is like" criterion. Next, read the section that introduces the bat example, from "I assume we all believe". Then, read the section where Nagel formalizes the argument about points of view, from "Whatever may be the status". Note his claim that for experience, unlike lightning, moving toward objectivity takes us farther away from the real nature of the phenomenon. Finally, read the short passage beginning "In a sense", which concludes that the species-specific viewpoint, which is omitted in successful reductions of external phenomena, is the very essence of the internal world.
Nagel’s argument is not that physicalism is definitively false. His more subtle conclusion is that we currently have no conception of how it could be true. The objective methods of science, as we understand them, are fundamentally unsuited to the task of explaining subjective reality.
2. The Knowledge Argument: Mary's Room
While Nagel's argument focuses on the nature of facts and explanation, Australian philosopher Frank Jackson formulated a related challenge in 1982 that focuses on the limits of knowledge. This is the famous "knowledge argument," best illustrated by the thought experiment of "Mary's Room."
The setup is as follows:
- Mary is a brilliant neuroscientist who has spent her entire life in a black-and-white room.
- Through black-and-white books and monitors, she learns everything there is to know about the physical world. She has complete physical knowledge, including the complete physics, chemistry, and neurophysiology of human color vision. She knows exactly what happens in the brain when someone sees a ripe tomato.
- If physicalism is true, and all facts are physical facts, then Mary knows everything there is to know about the world.
- The question is: If Mary is released from her room and sees a red tomato for the first time, does she learn something new?
It seems intuitively obvious that she does. She learns what it is like to see red. If she does learn something new, then she didn't know everything before her release. But she knew all the physical facts. Therefore, there must be non-physical facts, and physicalism is false.
Let's watch a detailed breakdown of this argument.
The Knowledge Argument Against Physicalism (Jackson - "What Mary Didn't Know")
The video "The Knowledge Argument Against Physicalism" from The Autodidact's Toolkit provides a clear, step-by-step reconstruction of Jackson's argument and its philosophical context.
Please watch these two key segments: Introducing Mary's Room (the thought experiment): This part introduces Frank Jackson and lays out the thought experiment. The Formal Argument (the knowledge argument): This segment presents the argument in its formal, premise-conclusion structure. Pay close attention to how the intuitive idea that Mary learns something is translated into a refutation of physicalism.
The power of the argument lies in its simplicity. It transforms the "explanatory gap" into an "epistemic gap"—a gap in Mary's knowledge. The core claim is that no amount of third-person, physical information can substitute for first-person, phenomenal experience. Jackson's own paper is remarkably concise and direct.
What Mary Didn't Know Frank Jackson The Journal of ...
This is Jackson's 1986 defense of his argument. It's a model of philosophical clarity.
Read the first page of the paper, from the beginning to the end of the section titled "I. THREE CLARIFICATIONS" (the whole first section). Here, Jackson presents the argument and, crucially, clarifies that the knowledge Mary lacks is not just about her own new experience, but factual knowledge about the experiences of others that she was studying all along.
3. Objections and Implications
Both Nagel's and Jackson's arguments have generated an enormous body of responses. Physicalists have, of course, tried to show where the arguments go wrong.
Perhaps the most famous objection to the knowledge argument is the "ability hypothesis." This response, championed by David Lewis among others, claims that Mary does not learn any new facts (knowledge-that). Instead, she acquires a new set of abilities (knowledge-how). She gains the ability to remember, imagine, and recognize the experience of red. Since abilities are not facts, her prior physical knowledge could still have been complete factual knowledge.
The other major line of response is to deny the central intuition: a physicalist might bite the bullet and insist that Mary learns nothing new. A person with truly complete physical knowledge would, in fact, know what it's like to see red, even without having the experience.
The Knowledge Argument Against Physicalism (Jackson - "What Mary Didn't Know")
Let's return to the Autodidact's Toolkit video, which does an excellent job of analyzing these replies.
Watch the final sections of the video: "Abortive" Replies (common flawed responses): This part is particularly useful for honing your argumentative analysis skills. It explains why simply saying "Mary didn't really have all the physical knowledge" is not a valid reply, because it fails to engage with the argument as presented. It also discusses the ability hypothesis. Acceptable Replies (potential valid responses): This segment explores the more sophisticated ways a physicalist might challenge the argument's premises, including the bullet-biting strategy that Mary learns nothing new.
Though they take different paths, Nagel's argument from subjective facts and Jackson's argument from incomplete knowledge both converge on the same conclusion: the phenomenal character of experience represents a feature of the world that seems to lie outside the scope of a purely physical description. They are formal articulations of the central challenge posed by the hard problem of consciousness.
Conclusion
In this lesson, we have moved from the general formulation of the hard problem to two specific, powerful arguments that use it to challenge physicalism.
- Key Takeaways:
- Thomas Nagel's "What is it like to be a bat?" argues that consciousness is defined by its subjective character of experience—the "what-it's-likeness."
- Nagel contends that facts about subjective experience embody a particular point of view.
- Since science's goal is to achieve an objective, third-person perspective that transcends individual points of view, it is methodologically incapable of capturing the essence of consciousness. To explain consciousness objectively is to explain it away.
- Frank Jackson's "knowledge argument" uses the Mary's Room thought experiment to create an epistemic challenge to physicalism.
- It argues that if a person with complete physical knowledge can still learn something new upon having a new experience (like seeing color), then there must be non-physical facts.
- These arguments attempt to show that qualia (phenomenal properties) are real, irreducible features of the world that are not captured by a complete physical story.
Preview of the Next Lesson:
Our discussion so far has focused on the phenomenal aspect of consciousness—raw feeling. But what about the cognitive aspect of the mind—thinking, understanding, and intelligence? A different kind of challenge to physicalist theories of the mind comes from the computational theory of mind, which models thinking as a form of symbol manipulation. In the next lesson, we will analyze John Searle's famous "Chinese Room" argument, which attacks the claim that a computer running the right program could ever truly understand anything.