The argument from essential external directedness against the internal physical state view

The argument from essential external directedness against the internal physical state view uses a simple logical rule called Leibniz’s law. This rule states that if what is true of A is not true of B, then A -A B. The argument says that different things are true of types of experiences and types of neural states, so they cannot be literally one and the same:

• (1) A correct definition of what it is to have the orange-experience will include the spatial terms round and moves to the right.
• (2) This is not true of the underlying neural state N. It is not the case that a correct definition of neural state N will include the spatial terms round and moves to the right.
• (3) Therefore, having the orange-experience is not identical with the underlying neural state N, even if it may be dependent on that neural state.

To appreciate the argument, look at Figure 2.3 illustrating the orangeexperience. Premise 1 says that a definition of what it is to have the orange-experience will include the spatial terms round and moves to the right. This is just our “simplified” formulation of essential external directedness. It is pretheoretically very plausible. Now look at Figure 2.1 illustrating neural pattern N. Premise 2 says that neural pattern N is different. No definition of what it is to undergo the neural pattern N will include the spatial terms round and moves to the right.⁶ Because different things are true of them, having the orange-experience cannot be identical with undergoing neural pattern N, even if they are intimately connected. Because it concerns spatial features, we might also call this the spatial argument against the internal physical state view.

At this point, the internal state theorist might respond as follows:

I want to agree with premise 1. But what is the case for premise 2? Why can’t I just reject it? Of course, undergoing the neural pattern N doesn’t involve the real existence of a round thing in the brain moving to the right. But why can’t I say -contrary to Premise 2 - that part of the essence of undergoing the neural pattern is that it involves there seeming to be a round thing moving to the right? In that case, the argument collapses. The internal physical state view is totally consistent with essential external directedness.

Here is the reason why the internal physical state theorists cannot make this response. Look again at Figure 2.1. What it is to undergo the neural pattern can be completely described in terms of types of neurons and the times, directions, and intensities at which they fire. This is just what it is to be a neural pattern. Therefore, in accordance with premise 2, the definition of what it is to undergo the neural pattern can be given without mentioning spatial terms round or moves to the left. (It is true that states can have hidden essences but we know that the essence of the neural pattern doesn’t involve these spatial features.) This rules out the response that it is part of the definition of undergoing the neural pattern that it involves the seeming-presence of a round thing moving to the right.

The argument from essential external directedness against the internal physical state view is analogous to an argument that all will accept:

• (1) A definition of what it is to think that something is round and moving to the right will mention round and moving to the right; for to think this is to attribute round and moving to the right to something.
• (2) This is not true of making the noise “something is round and moving to the right"; this noise can be fully characterized without mentioning the spatial features round and moving to the right.
• (3) So to think that something is round and moving is not just to make the noise “something is round and moving”; it might sometimes involve making this noise, but it is something more than making this noise.

Suppose we accept the argument from essential external directedness against the internal physical state view. What alternative view might we accept? What views are consistent with essential external directedness?

In fact, all the other views we discuss in this book endorse the argument and its conclusion:

Sense datum view. To have the orange-experience is to experience a sense datum that is orange, round, and moving to the right, in accordance with essential external directedness. By contrast, neural states can be defined entirely in terms of types of neurons and the times, directions, and intensities at which they fire. So, on the sense datum view, to have the orange-experience is not just to have a neural state, since they have different definitions. The orange-experience is dependent on a neural state, but it is something more than a neural state.

Representational view. To have the orange-experience is to "experientially represent" that something is orange, round, and moving to the right. (If someone has the orange-experience in a hallucination, there is in fact no such object - not even a “sense datum”.) So spatial terms enter into a definition of what it is to have the orange-experience. This is not true of any neural pattern. So, on representationalism, to have the orange-experience is not just to have some neural state. The orangeexperience may be dependent on a neural state, but it is something more than a neural state. To define what it is to have this experience, neural terminology is insufficient. We must mention that the neural state enables one to “experientially represent” a round thing that is moving to the right.

Contemporary naive realism. To have the orange-experience is to either really experience an external physical thing that is orange, round, and moving to the right (in normal perception) or to be in a state that is indiscriminable from experiencing such a thing (in illusion or hallucination). Since this is not the definition of any neural state, to have the orange-experience is not just to undergo a neural state. The orange-experience is something more than a neural state.

All these views endorse essential external directedness because the terms round and moves to the right show up in their definitions of what it is to have the orange-experience. Notice that the “representational view” rejects the act-object assumption. Contemporary naive realism also rejects the act-object assumption in the case of hallucination. This reinforces the point (made in the previous section) that essential external directedness is not committed to the general act-object assumption.

Let me conclude with some comments.

First comment. There is a long history of Leibniz’s law arguments against the identification of experience-types with internal neural-types (Smart 1959). For instance, suppose that you smell some mint tea. Against the internal physical state theory, it might be argued that your sensation involves the smell quality minty, but your underlying neural state S doesn’t involve this smell quality (just neuronal firings), so they cannot be one and the same. But the “spatial” Leibniz’s law argument above is superior to this traditional kind of Leibniz’s law argument. For in response to this traditional Leibniz’s law argument, the internal physical state theorist can say that the neural state S does essentially involve a minty smell quality, because that smell quality itself just is a neural pattern involved in S (even if this is not evident to you). By contrast, a parallel response to the spatial Leibniz’s law argument above is not possible. For no one thinks that the spatial features round and moving to the right involved in the orangeexperience turn out to be neural properties involved in the underlying neural state N!

Second comment. The argument from essential external directedness is only supposed to rule out the internal physical state view, which makes the strong claim that all experience-types are identical with neural-types. By this argument, experiences and neural states have different natures. So even if neural states are sufficient for experiences, experiences cannot be identical with neural states.

The argument from essential external directedness is not meant to rule out experiential internalism - the weaker claim that, for every experiencetype, there is an internal neural-type that is necessarily sufficient for it. In fact, it doesn’t rule out experiential internalism. This is good, because experiential internalism is a popular idea.

To see that the argument from essential external directedness does not rule out experiential internalism, notice that there are views that accommodate experiential internalism but that are not ruled out by essential external directedness. One such view is the sense datum theory (see especially Box 1.1 in Chapter 1). On this view, the orange-experience depends on a neural pattern but it has a different nature from the neural pattern: it is a relation to a round and moving sense datum. So, unlike the underlying neural pattern, the experience is essentially externally directed.

Another such view is “internalist representationalism”. We already mentioned this view’ in passing in Section 2.2 and will consider it in detail in Chapter 4. On this view, too, the orange-experience depends on the neural pattern, but it has a different nature from the neural pattern: it consists in experientially representing a round and moving thing. So, unlike the underlying neural pattern, the experience is essentially externally directed. In this way, unlike the internal physical state view, internalist representationalism allows us to hold that experience is both internally dependent in a strong sense and essentially externally directed.

Third comment. It may be that the only way for internal physical state theorists to save their view in the face of this argument would be to deny premise 1. If this is right, then the internal physical state view requires that it is not the case that spatial terms like round and moving to the left enter into a correct definition of what it is to have the orange-experience (because they don’t enter into a definition of what it is to have the neural pattern with which this type of experience is identical). It is worth pausing for a moment to appreciate what this would amount to.

Return to an example we have already used before: having a diffuse headache. Clearly, you can define what it is to have an experience with this character without using the spatial terms round and moving to the right. So if the internal physical state view implies the rejection of premise 1, then what it implies is that having the orange-experience (Figure 2.3) is like having a headache in this respect. And this amounts to saying that the experience “really” has a character other than the character it seems to have. For it certainly seems to have a character radically different from the character of a headache, a character that can only be defined by using spatial terms like round and moving to the right.⁷

In Section 2.7, we will explore the question of whether internal physical state theorists might block the argument by denying essential external directedness. However, let us first put another argument on the table.