Putnam's Objection to Turning's Test 


We "cannot attribute reference to machine."
 
That means: 
 
 "What is needed is evidence that the (machine) uses its words to refer to things
in the world, that its predicates are true of things in the world, that it knows
the truth conditions of its sentences."

How do human beings have this kind of knowledge of reference? Here is a sketch of
Putnam's argument (not in our reading assignment).

Words or pictures do not intrinsically represent what they are about. 

That is, the internal features of these words or pictures do not represent. 

For representation depends upon convention. 

What's required for reference is that there be some causal connection between the
representation and what it represents. Humans use words to refer to things in the
world which they view and manipulate. So, we know that

'water quenches thirst' 

is true because we find from experience what water quenches thirst. 

But knowing that requires knowing the reference of these words. 


Consider the brain in a vat. 

Your brain is kept alive in a vat of nutrients, and the nerve endings are
connected to a computer which cases the brain to have the illusion that
everything is normal. 

(This is a variation on Cartesian skepticism as presented in the 1st Meditation.)

"The computer is so clever that if the person tries to raise his hand, the
feedback from the computer will cause him to 'see' and 'feel' the hand being
raised."

The brain in the vat is like the computer. It is not connected to the external
world. That means, none of the words it uses refer to things in the real world;
its words (or pictures) only seem to refer. 

"There is some causal connection between the machine and the real world... via
the perceptual experience of knowledge of the creator-designers. But such a weak
connection can hardly suffice for reference." 

To see why this is correct, consider again the brain in a vat. It cannot think
about things in the world because it cannot represent things in the world. The
brain in the vat's words (or pictures) do not represent anything because they are
not casually connected with the world in the right way. (The connection via the
computer is too weak to count as such a connection.) 

The brain in the vat cannot know that


'water quenches thirst' 

is true because it does not know from experience what water quenches thirst. It
only seems to have these experiences. 

We don't consider all of Putnam's argument. To work this account out in more
detail we would have to discuss the difference between

	Knowing that a word represents something in the world

And

Having the illusion that a word represents something
Putnam's Objection to T