Kaganos Brain in a vat A similar argument can be given for thought contents expressed by use of indexical pronouns and natural kind terms. Request removal from index. Second, the person being addressed can be taken to be avt premise 1 merely for the sake of conditional proof. In other projects Wikimedia Commons. What is important is the idea that the truth-conditions would be non-standard, as in: The Brain as Metaphor in Digital Culture.
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Skeptical Hypotheses and the Skeptical Argument The Cartesian skeptic puts forward various logically possible skeptical hypotheses for our consideration, such as that you are now merely dreaming that you are reading an encyclopedia entry.
The more radical Evil Genius hypothesis is this: you inhabit a world consisting of just you and a God-like Evil Genius bent on deceiving you. In the Evil Genius world, nothing physical exists, and all of your experiences are directly caused by the Evil Genius. So your experiences, which represent there to be an external world of physical objects including your body , give rise to systematically mistaken beliefs about your world such as that you are now sitting at a computer. Some philosophers would deny that the Evil Genius hypothesis is genuinely logically possible.
Materialists who hold that the mind is a complex physical system deny that it is possible for there to be an Evil Genius world, since, on their view, your mind could not possibly exist in a matterless world. Accordingly, a modern skeptic will have us consider an updated skeptical hypothesis that is consistent with materialism.
Consider the hypothesis that you are a disembodied brain floating in a vat of nutrient fluids. This brain is connected to a supercomputer whose program produces electrical impulses that stimulate the brain in just the way that normal brains are stimulated as a result of perceiving external objects in the normal way. If you are a brain in a vat, then you have experiences that are qualitatively indistinguishable from those of a normal perceiver.
If you come to believe, on the basis of your computer-induced experiences, that you are looking at at tree, then you are sadly mistaken. After having sketched this brain-in-a-vat hypothesis, the skeptic issues a challenge: can you rule out the possibility described in the hypothesis? Do you know that the hypothesis is false? The skeptic now argues as follows. Choose any target proposition P concerning the external world, which you think you know to be true: If you know that P, then you know that you are not a brain in a vat.
You do not know that you are not a brain in a vat. So, You do not know that P. Premise 2 is backed by the consideration that your experiences do not allow you to discriminate between the hypothesis that you are not a brain in a vat but rather a normal human from the hypothesis that you are a brain in a vat. Your experience would be the same regardless of which hypothesis were true. So you do not know that you are not a brain in a vat. Imagine that you are a brain in a vat in a world in which the only objects are brains, a vat, and a laboratory containing supercomputers that stimulate the envatted brains.
Imagine further that this situation has arisen completely randomly, and that the brains have always been envatted. A skeptical argument just like that above can be formulated using the BIV hypothesis.
Putting things now in the first person, Putnam argues that I can establish that I am not a BIV by appeal to semantic considerations alone — considerations concerning reference and truth. This will block the BIV version of the skeptical argument. Here is how Putnam motivates his anti-skeptical semantic considerations.
Suppose that there are no trees on Mars and that a Martian forms a mental image exactly resembling one of my tree-images as a result of perceiving a blob of paint that accidentally resembles a tree. This is due to the lack of any causal connection between the image and trees even, we will suppose, any attenuated causal connection such as interaction with a visiting Earthling who has seen trees.
Neither of us would have the sort of causal contact with trees which is required for our images to refer to trees. Call these considerations about reference and truth semantic externalism. This view denies a crucial Cartesian assumption about mind and language, viz. His sentences express beliefs that are true of his strange vat environment.
If DA succeeds, then we have a response to a skeptical argument involving the BIV hypothesis which shares the form of the Cartesian argument 1 - 3 above. Step h itself follows from g on natural assumptions about negation, truth, and quotation, but T is problematic in the current anti-skeptical context.
The assumption of T seems to beg the question against the skeptic. But that is what the anti-skeptical argument was supposed to prove. So, I am not a BIV. I am thinking that trees are green. So, F. I am not a BIV. We will discuss E below. SA2 highlights the connection between semantic externalism and the mind. The arguments rest only upon the claim that the referents and contents in question differ from my referents and contents.
Objections and Responses Let us now turn to an objection to SA1. Though the argument does not obviously require knowledge that I am a non-BIV speaking English , as Supplemented DA seemed to, its premise B does seem upon reflection to be question-begging. So, C. But a problem still remains. A similar worry can be laid at the door of SA2. In order to know its second premise, E , I need to know what I am now thinking. So in order to know what I am now thinking in order to know that I am thinking that trees are green , it seems that I need to know that I am not a BIV thinking a thought with a strange content.
A reasonable response to the foregoing objection to Modified SA1 is as follows. But I do know certain things about my own language whatever it is and wherever I am speaking it. This is a priori knowledge of semantic features of my own language whatever it is — English or vat-English. A similar response to the foregoing objection to SA2 is that I have knowledge of my own mind that is not experientially based. I can gain the knowledge that I am now thinking that trees are green via introspection.
A problem for this response has been raised by various philosophers. It has been suggested that semantic externalism engenders severe limits on self-knowledge: if I do not know that I am not a BIV, then I do not know which contents my thoughts possess: the normal ones that I think that they possess, or the strange ones that they possess if I am a BIV.
So the response we have considered may be in trouble if semantic externalism gives rise to such skepticism about knowledge of content. The foregoing defenses of the Simple Arguments emphasize a constraint on anti-skeptical arguments: their premises must be knowable a priori. The justification of their premises must not require any appeal to the deliverances of sense-experience.
This thought in turn rests upon the natural assumption that trees are not computer program features. But is that assumption something that I know a priori? In work unrelated to skepticism, Putnam has claimed that even though it is necessary that cats are animals just as it is necessary that water is H2O , it is not knowable a priori that cats are animals just as it is not knowable a priori that water is H2O.
According to Putnam, the concept of cat allows that in advance of gaining knowledge of their inner structure, cats could turn out to be robots. The worry is that in a similar way, the concept of tree is such that in advance of gaining knowledge of the existence and nature of trees, trees could turn out to be computer program features. If I hold in abeyance my seeming a posteriori knowledge about trees, then, I cannot fairly say that in the vat world, there are no trees.
This objection to Modified SA1 can be answered by focusing upon the dialectical situation between skeptic and anti-skeptic. The skeptic wishes to impugn my seeming knowledge of the external world by putting forward a skeptical hypothesis that is incompatible with the external-world propositions I believe.
On the current objection to our anti-skeptical argument, the skeptical critic undermines his own position by suggesting that SK is compatible with external-world propositions such as that I am in the presence of green trees. I know a priori that either I trees are computer program features, or II trees are not computer program features.
So we could view Modified SA1 as being an argument by cases: it is not known a priori which case obtains, but it is known a priori that the skeptic loses in each case.
Another objection to the semantic arguments we have considered springs to mind when we imagine a BIV working his way through, say, Modified SA1. Understood in this way, his second premise is true. The following worry arises. However, this worry is unfounded.
Just read the argument carefully when you work through it! It makes no difference to my argumentative situation if someone on Alpha Centauri uses those very sentences with different meanings from mine and proves that muons move rapidly. A final objection to the semantic arguments is hard to dispute. The problem is the narrow scope of the arguments.
If I have been speaking English up until my recent envatment, then my words will retain their English referents to trees and so on and my thoughts will retain their normal contents about trees and so on. Thus, the Putnamian semantic externalist considerations will find no purchase against the skeptical hypothesis that I am a fledgling brain in a vat. The semantic externalist would say that in such a vat world, my words fail to refer to things in my world, and no truth conditions can be properly assigned to my sentences.
These sentences accordingly fail to express contentful thoughts. On this radical brain-in-a-vat hypothesis, I am asked, then, to countenance the alleged possibility that I am not thinking contentful thoughts via meaningful sentences with reference and truth conditions. Thus, this radical skeptical hypothesis may well in the end undermine itself.
Conclusion The brain-in-a-vat hypotheses are crucial for the formulation of skeptical arguments concerning the possibility of knowledge of the external world that are modeled on the Cartesian Evil Genius argument.
Even if Putnamian arguments fail to rule out all versions of the brain-in-a-vat hypotheses, their success against the radical BIV hypothesis would be significant.
Further, these arguments highlight a novel view of the relations between mind, language, and the external world. Alston, W. Brueckner, A. Stern ed. Bernecker and D. Pritchard eds. Christensen, D. DeRose, Keith, and T. Warfield eds. Ebbs, G. Forbes, G. Gallois, A.
Brains in a Vat