Knowledge Arguments

Knowledge arguments begin from an apparent limit on objective information. A person could know every physical truth about an experience while never having undergone it. When the experience first occurs, they appear to learn something. If all physical facts were already known, the new knowledge seems to concern a non-physical fact.

Frank Jackson's story of Mary the colour scientist is the canonical case. Its force comes from separating three questions often run together: whether Mary gains anything, whether what she gains is propositional knowledge, and whether a new proposition requires a new property. Almost every reply accepts the first claim and blocks a later step.

Mary in the monochrome room

Mary is a brilliant scientist confined from birth to a black-and-white environment. She learns every physical fact about colour vision: optics, retinal processing, neural dynamics, discrimination, memory, language, and behaviour. On release she sees a red object for the first time.

The argument is:

1. Before release, Mary knows all physical facts about human colour vision.
2. On seeing red, Mary learns what it is like to see red.
3. Therefore Mary learns a fact she did not know before.
4. Therefore not every fact is a physical fact.
5. So reductive physicalism is false.

The intuition behind premise 2 is strong: Mary's epistemic situation changes. The controversy begins with how to classify the change and what follows from it.

What does "all physical facts" include?

The setup idealises aggressively. If Mary knows every physical fact, does she know facts about her own future brain, every counterfactual, every indexical truth, and every functional relation? If phenomenal truths are physical truths under another mode of presentation, the premise may already include what the conclusion says is absent.

The thought experiment is not intended as an achievable curriculum. It asks whether third-personal structural and dynamical knowledge entails first-personal knowledge. Adding more textbooks of the same objective kind does not appear to teach what red looks like. A reply should explain the kind of epistemic difference rather than dismiss the scenario as practically impossible.

The ability hypothesis

David Lewis and Laurence Nemirow argue that Mary gains know-how, not a new fact. She acquires abilities to recognise, imagine, remember, and compare red experiences. One can know every proposition about swimming without knowing how to swim; gaining the ability does not reveal a non-physical fact.

The reply preserves physical completeness and explains why experience is required. Abilities often need training or direct acquaintance even when the relevant facts are known.

Objections note that Mary seems able to learn something even if an injury prevents her from remembering or imagining red afterward. She can also truthfully think "so this is what seeing red is like," which appears propositional. The ability theorist can allow associated judgments while insisting their content was already known, but then must explain the apparent discovery.

Acquaintance

The acquaintance hypothesis says Mary enters a new direct relation to an old property. Knowing a person by description differs from meeting them; acquaintance adds an epistemic relation without adding an individual to the world. Likewise, seeing red acquaints Mary with a physical property she previously knew descriptively.

This captures the first-personal change better than ability alone. It also explains why no amount of testimony substitutes for the experience. The challenge is whether acquaintance itself carries new propositional knowledge. If Mary can now distinguish possibilities she previously could not, the anti-physicalist argues that her factual information has increased.

The reply can accept new de re or indexical knowledge while denying a new non-physical property. Learning "I am that person" adds self-locating knowledge although every non-indexical fact was available. The question is whether phenomenal knowledge has this structure.

Old fact, new mode of presentation

On the new-mode response, Mary knew one property physically and now knows it phenomenally. The same fact is presented through different concepts:

$$\text{neural/functional concept}⟶P⟵\text{phenomenal concept}.$$

Identity does not require cognitive equivalence. Someone may know that Hesperus appears at dusk and later learn that Phosphorus, seen at dawn, is the same planet. In Mary's case, however, the subject is stipulated to know every physical identity. The response must explain why phenomenal concepts cannot be derived even from complete physical knowledge.

The standard answer is that phenomenal concepts are recognitional or demonstrative, formed through the experience itself. Their acquisition condition explains the epistemic gap without an ontological gap. Critics object that the account invokes the special phenomenal state to explain a concept while leaving the state's physical nature unexplained.

The phenomenal-concepts strategy

The strategy generalises the new-mode reply. Phenomenal concepts may quote an experience, classify by resemblance to a current sample, or refer directly without descriptive content. Physical concepts classify through causal and structural theory. Because the two concept families differ, no a priori entailment connects them even if they refer to one property.

This predicts Mary's surprise and her inability to imagine red before release. It also explains why the explanatory gap feels unlike ordinary scientific identities.

Its vulnerability is the explanatory gap within the explanation. Why does this physical recognitional mechanism yield a concept with the distinctive first-personal character? If the answer cites the phenomenal property irreducibly, the strategy is compatible with dualism; if it cites only function, critics say it explains access to the concept but not experience.

No new propositional knowledge

Some physicalists deny premise 3 directly. Mary can truthfully express new sentences after release, but their propositional content may be old. She gains a token-demonstrative way to think "this kind of state" and can connect it with old descriptions.

The proposal resembles indexical ignorance. A person who knows a complete impersonal map may still learn "I am here" without discovering a new non-geographic property. Likewise Mary locates herself within the physical facts she already knew.

The analogy is imperfect. Indexical information selects a position in an antecedently understood structure. Mary's new knowledge appears to disclose the character of a state, not merely which state she occupies. The physicalist must show that all such character was already represented structurally, though inaccessible under the first-person mode.

Jackson's later physicalism

Jackson eventually rejected the anti-physicalist conclusion. He treated the argument's force as evidence that our intuitions about phenomenal information are misleading, not that physicalism is false. Representational accounts of experience helped motivate the change: if phenomenal character is exhausted by representing worldly properties in a certain way, Mary's physical knowledge can include the represented facts while release changes her representational abilities.

An author's change of mind is not an argument, but it illustrates that accepting the intuition of epistemic novelty does not force property dualism. The inferential bridge from epistemology to ontology remains the entire issue.

Variants

Related cases alter the sensory modality or subject. A congenitally blind expert learns about vision, a deaf scientist learns sound, or a person learns echolocation. The bat discussion emphasises that another form of life may remain imaginatively inaccessible even with complete objective knowledge.

These variants test whether the argument depends on colour vocabulary or on a general feature of perspective. They also reveal a limit: failure to imagine an experience can show missing ability or acquaintance without showing that no objective structural description is complete.

What the argument establishes

The argument securely establishes a difference between learning through description and learning through experience. It less securely establishes new propositional knowledge, and only with an additional premise establishes non-physical facts.

The knowledge argument is therefore not one intuition but a sequence of bridges. Its lasting value is forcing physicalism to explain why complete objective knowledge would not confer phenomenal understanding automatically.

Selected references

• Jackson, Frank. "Epiphenomenal Qualia" (1982).
• Lewis, David. "What Experience Teaches" (1988).
• Loar, Brian. "Phenomenal States" (1990/1997).
• Nemirow, Laurence. "Physicalism and the Cognitive Role of Acquaintance" (1990).
• Papineau, David. Thinking about Consciousness (2002).