The Logical Possibility of Physically Identical Worlds with Different Conscious States 

Premise 1: It is logically possible to conceive of a possible world (PW) that is physically identical to ours but where the conscious experience is either (1) entirely lacking or (2) qualitatively different.

• Case 1 (Lack of Consciousness): In this possible world, all physical processes and structures (e.g., brain activity, neural networks) are identical to ours, but there are no conscious experiences at all. 
  
  
• Case 2 (Different Conscious States): In this possible world, all physical processes and structures are identical to ours, but the conscious experiences associated with them are different (e.g., pain might feel like pleasure, or redness might appear as greenness). 

Premise 2: If such possible worlds are conceivable and coherent, it follows that the physical facts alone do not determine the conscious facts. 

Premise 3: Conscious facts must then be "further facts," distinct from and not reducible to physical facts. This means: The same physical facts can result in no conscious states (consciousness is absent despite physical processes being present).The same physical facts can result in different conscious states (consciousness varies even when physical processes are identical). 

Premise 4: Both scenarios are logically possible and undermine the central claim of materialism: that physical facts wholly determine all facts about the world, including consciousness. 

Conclusion: Materialism is false because it cannot account for these logical possibilities. Materialism asserts that all facts are physical facts, but the conceivability of these possible worlds shows that consciousness cannot be fully explained by or reduced to the physical domain.

A beginner-friendly explanation of the argument:

The Problem with Materialism

Materialism says that everything about the world, including our thoughts and feelings (consciousness), can be fully explained by physical things like atoms, neurons, and brain processes.

But there’s a problem with this idea:

1. Imagine This Scenario:
   • There could be a world just like ours where everything physical is identical (same atoms, same brains, same bodies).
   • But in that world, either:
     • There’s no consciousness at all (people act like us but feel nothing).
     • Or the consciousness is completely different (pain feels like pleasure, red looks like green).
2. What This Means:
   • If this kind of world is possible, then consciousness doesn’t depend only on the physical stuff.
   • Physical facts (like how the brain works) don’t tell the whole story about what it’s like to be conscious.
3. The Big Takeaway:
   • Materialism is wrong because it can’t explain how the same physical facts could lead to no consciousness or different kinds of consciousness.
   • Consciousness must be something extra—something more than just physical facts.

Why This Points to Dualism

If materialism is false, we need another explanation for consciousness. Dualism is the idea that the mind and body are two separate kinds of things. The physical brain handles the material stuff, but consciousness is something non-physical.

Since materialism can’t explain consciousness, dualism starts to make a lot more sense. It says that consciousness isn’t just a byproduct of the physical world—it’s its own kind of reality.

In Short:
We can imagine a world where everything physical is the same as ours, but consciousness is missing or different. This shows that consciousness can’t be fully explained by physical facts. Materialism is wrong, and dualism is likely true because it treats consciousness as something more than just physical processes.