Here is a famous painting by French surrealist Rene Magritte: http://www.thirdwave-websites.com/blog/map-is-not-the-territory-this-is-not-a-pipe.jpg Think about this. Most the time the word we use comes with an image that appears in our minds. I say "cat" and I picture some generic version of a cat. Now tell yourself: "This is not a cat." IOW, the cat--the real animal the word "cat" is referring to--is NOT this image inside your head. How then can the word "cat" refer to the real physical animal but NOT the mental image of that animal? Two levels of representation perhaps? The word represents the image and the image represents the animal. But does the word "cat" even represent anything real and physical. I can definitely ostensively define, or use examples of, the word "cat" ("A" cat or "THIS" cat or "THESE" cats) but never do I see just "cat"--the precise thing that the generic image in my head is referring to. The image therefore represents not an example or a member of a set but a set itself--a conceptual generalization that does not exist in physical reality. From the word "cat" to the image of "cat" to the general abstract concept or set called "cat". When does the word cat EVER represent a real physical cat?