A Philosophical Zombie
Are human beings defined by their physical attributes? Descartes thought humans, unlike animals, cannot be fully explained physically. We have something beyond our bodies that enables us to think and feel. Cognitive understanding, mental development; the unique ability to contemplate is what largely separates you and I from animals and other conscious objects.
With the development of science and technology, the idea that science could explain everything grew bigger. Physicalists would say yes, while Descartes would say no. Physicalism is the hypothesis that everything is physical. It means there would be no Psyche, but only our bodies. A philosophical zombie then emerged to counter physicalism.
A philosophical zombie is a being who is the same as us physically but lacks qualia. The most widespread and vast definition of qualia is a phenomenal character. Imagine yourself eating an apple. Whether it is about the apple's color, taste, or texture, you are bound to feel something about that apple. That thought is what we call qualia. Simply put, a zombie does not have a consciousness. Of course, they are not possible in the real world. A zombie is like an AI programmed to look like a human. However, what the pro-zombie argument is about is whether it is conceivable.
David Chalmers, who came up with the term philosophical zombie, goes on his argument in the following way. P: Philosophical zombies are conceivable. Q: Everything conceivable is possible. P->Q: Zombies are possible. Thus, not everything is physical, and physicalism is wrong.
Some have countered this argument in two ways. First: Philosophical zombies are not conceivable. Our feelings are about neuron activation and hormones. As zombies are the same as us in every physical way, it must feel something. It is a thesis that does not make sense, such as a round square. Second: Not every conceivable thing can exist. Imagine yourself going back to 10,000 years with a time machine. You ask a mathematician then whether the largest prime number exists. He would say yes and conceive of the number. But we now know there is no such thing as the biggest prime number. Also, we conceive some thoughts like 'What if~?' What if WW2 never happened? What if this person became a president instead? We always think like this despite it being impossible.
Sure, anti-physicalists can defy these counterarguments. For example, they could assert that we are not conceiving those questions. We are simply thinking of a superficial concept of them. Chalmers himself argues for the conceivability of zombies. Imagine replacing your brain with tiny homunculi. They maintain your body's function. Also, each of them uses a cell phone to act as a neuron. Would your mind still be conscious?
While many instinctively say no, some physicalists would say yes. However, the point here is that we can conceive of non-conscious humans. The only things that differentiate you from a zombie are neurons and homunculi. If you can conceive this, you can also conceive a zombie.
Chalmer eventually leads this argument to the so-called hard problem. It aims to explain how physical beings can be conscious rather than non-conscious. Physical problems, unlike consciousness, can be analyzed by reductive explanation. To do a reductive explanation, we need two premises. The first presents a functional analysis of the target phenomenon. The second is about a realizer of the functionally characterized target. The example is the following: 1. The gene is the unit of hereditary transmission. 2. Regions of DNA are the unit of hereditary transmission. 3. Therefore, the gene is a region of DNA. Why cannot this reasoning explain consciousness? According to Chalmers, it is because consciousness cannot be analyzed functionally. If we can analyze it, the zombies would not be conceivable. We can conclude that we either eliminate consciousness or add consciousness to our ontology on par with some reality, such as gravity.