I recently posted an argument for property dualism. Here I shall present another one.
The thought/belief that I have that philosophy is the highest good is an event to which I have privileged access. But suppose the event that is my having this belief just is a physical event. What would this event be on physicalism? This event would have neurophysiological properties and would probably consist in a large number of neurons firing and doing various things. It will also have to have propositional and semantic content if we are to call it a belief. So here is the question. If we were to isolate this event (the neural event) such that we would know everything about it would we be able to give a complete, true description of the thought/belief?
It seems not. For my belief has propositional and semantic properties that cannot be known by observing a neural event. By observation we might be able to explain where each neuron was at some time, and to which synapses it is connected, and its various relations to other parts of the body. We might be able to know similar things about sets of neurons at work. But we wouldn't know that this event was in some way representative of the belief that philosophy is the highest good. Similarly, if I have an vivd image in my mind of a sunset, no amount of observation of the goings on in my brain will entail the knowing of or "seeing" of the image. So knowing everything about some physical event in my brain doesn't entail knowing everything about my thought, or knowing everything about my image of a sunset (knowledge here includes the experience of the image). So I conclude, where N = some physical event in my brain and T = my thought/image, etc.:
(1) It is false that (you know everything about N) entails (you know everything about T).
So now we can produce an argument:
(E) For all x and y, if x = y, then, for any person P, P knows everything about x just in case P knows everything about y.
This is a formal way of saying that if x = y then if you know everything about x then you know everything about y and vice versa. Now, we have established, I think, that complete physical knowledge about some event in my brain that is correlated with some mental event (my thought) doesn't entail complete knowledge. For you can know everything about this neural event and that knowledge won't entail your knowing the semantic and propositional contents of the thought I am having. You won't be able to, just by looking at my brain, give a complete, full description of my thought. In order for you to be able to do this I must tell you what my thought is.
(2) You know everything about N and you don't know everything about T.
This follows from (1). Let P = "you know everything about N" and Q = "you know everything about T." By (1), ~(P entails Q). So, ~(~P v Q). So, (P & ~Q). This just is "You know everything about N and it is false that you know everything about T. This just is (2).
(3) Suppose N = T. [ASM]
(4) Then, for any person P, P knows everything about N just in case P knows everything about T. [from E and 3]
(5) You know everything about N. [from 2]
(6) Therefore, you know everything about T. [from 4 and 5]
(7) You don't know everything about T. [from 1]
Since this is a contradiction, we negate our assumption. Hence:
(8) Therefore, it is false that N = T.
But, if T isn't identical with any physical event, then T just is a nonphysical event. So far we have event dualism. What is an event? Events are properties instantiated in substances at times. What makes an event a physical event is that the instantiated properties are physical properties. What makes an event a nonphysical event is that the instantiated properties are nonphysical properties. So, given that there are nonphysical events, there are also nonphysical properties. These events and properties are mental events and mental properties. So both property and event dualism are true.
One might argue that scientists are able to tell us what we are thinking by observing brain patterns, or goings on in the brain. The idea here is that thoughts of a kind k are correlated with neural events of a kind k*. So scientists can say that k when they observe k*. But I don't see why this will work. Scientists don't know that k in virtue of the fact that they know that k* alone. They know that k because they know that k is correlated with k*. They know that k is correlated with k* in virtue of the fact that people report their thoughts and scientists are able to see what happens in their brains when they are thinking.
One might also argue that there might be technology in the future that enables scientists to "read our minds." But this just begs the question. You won't be able to know that I am thinking that philosophy is the highest good just by looking at neurons firing about. This is evident once we realize that different people can have the same thoughts. We can have the same thoughts but different neural events. So how will scientists be able to identify our thoughts with neural events? There can be different neural events for the same thoughts. So this objection isn't very compelling.
In case the above argument isn't convincing, I shall reiterate (briefly) the argument for property dualism in the other post (see link above). Physical events are events to which the subject doesn't necessarily have privileged access. Mental events are events to which the subject necessarily has privileged access. Since something is true of all mental events that is untrue of all physical events, they cannot be the same thing. So mental events are distinct from physical events. It seems to me that these arguments are strong and I think most philosophers today (or perhaps a plurality) are inclined towards property dualism (even though most are still physicalists who think that mental events are ontologically dependent on physical substances/events). But might we get to substance dualism?
If I were a physical being what physical being would I be? It seems that I would be my brain, or some part of my brain. Let B = whatever physical being with which I am supposedly identical. Furthermore, a very brilliant neuroscientist named Jack knows everything about B. Suppose I = B. Then, by (E), Jack knows everything about B just in case Jack knows everything about me. So Jack knows everything about me. But, as I have already argued, Jack won't know T just by knowing some physical event in my brain (he knows this physical event in virtue of the fact that he knows everything about B). If Jack doesn't know that T, then Jack doesn't know everything about me; namely, he doesn't know about what thoughts I am having. So it is both true and false that Jack knows everything about me. Therefore, I =/= B. If I =/= B then there is nothing physical with which I am identical. Thus, I am identical with something nonphysical, which we all call the soul.
So I think we have a good argument here for substance dualism.
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