The Battleground of Mary's Mind
The debate between the Knowledge Argument and the Ability Hypothesis is one of the most significant clashes in the modern philosophy of mind. It centers on a single, crucial question: What exactly happens to Mary when she steps out of her black-and-white room and sees a red rose for the first time?
Both sides agree that Mary undergoes a profound change, but they disagree entirely on the nature of that change and what it means for the truth of physicalism.
The Knowledge Argument: Acquiring New Facts
Formulated by Frank Jackson, the Knowledge Argument claims that Mary's breakthrough is cognitive and factual. Before her release, Mary had complete physical knowledge, but she lacked propositional knowledge (knowledge-that) regarding color experience.
When she sees red, she learns a new proposition: "This is what it is like for humans to experience red." Because this is a genuine fact about the world, and because she did not know it despite knowing all physical facts, the Knowledge Argument concludes that there are non-physical facts. Therefore, physicalism is false.
The Ability Hypothesis: Acquiring New Skills
The Ability Hypothesis was developed by physicalist philosophers Laurence Nemirow and David Lewis to rescue physicalism from Jackson's conclusion. They argue that the Knowledge Argument relies on an equivocation of the word "know."
According to this view, there is a fundamental difference between two types of knowledge:
- Propositional Knowledge (Knowing-That): Knowledge of facts (e.g., knowing that water freezes at 0°C).
- Practical Knowledge (Knowing-How): Possession of an ability or skill (e.g., knowing how to ride a bicycle).
The Ability Hypothesis asserts that when Mary sees red, she does not learn any new facts about the universe. Instead, she simply acquires new abilities. She now knows how to visualize red, how to remember the color red, and how to recognize red objects in her environment. Since acquiring a skill is a physical process of neural rewiring, her new "know-how" does not require the existence of non-physical facts, leaving physicalism intact.
Comparison Table: Key Differences
| Feature | The Knowledge Argument (Jackson) | The Ability Hypothesis (Lewis/Nemirow) |
|---|---|---|
| What Mary Gains | New factual information (knowledge-that). | New practical abilities (knowledge-how). |
| Nature of the Gain | Cognitive discovery of a subjective truth. | Acquisition of recognition and imaginative skills. |
| Implication for Physicalism | Physicalism is false; physical facts do not cover all reality. | Physicalism is true; skills do not require non-physical facts. |
| Core Philosophical Focus | Qualia as non-reducible properties. | Cognitive functions and behavioral capacities. |
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Join NowCriticisms of the Ability Hypothesis
While the Ability Hypothesis is a clever defense of physicalism, it has faced strong pushback. Critics argue that it fails to capture the true nature of Mary's experience. When Mary sees red, she seems to make a genuine discovery about the world, not just gain a skill.
For instance, if Mary were offered a choice between seeing red or seeing blue before her release, and she chose red, her choice would be based on a desire to know what red is like—a factual curiosity—not merely a desire to acquire a sorting skill. This suggests that "knowing what it is like" cannot be entirely reduced to "knowing how to do."