If Cats Weren't Animals

The below is reproduced from a paper I wrote for a philosophy class, concerning topics I now find to be very interesting. The professor enforces all sentences to be no more than 16 words.

Below I will discuss Hilary Putnam's robot cat thought experiment. This appears in his 1962 article “It Ain't Necessarily So.” I will first describe the thought experiment, and then I will review its implications.

The thought experiment goes as follows. Suppose in an alternate world, the creatures people call “cats” are not actually cats. Instead, they are mechanical robots placed onto Earth by deceptive Martians. These robots are not alive, even though they appear to be. They demonstrate convincing illusions of all biological behaviors, such as eating and reproduction. Everyone in the alternate world, including the scientific community, mistakes the robots for biological cats. Further, suppose in this world that there were never any living cats. That is, at no point in time did evolution ever produce any cats. From the very beginning, there were only ever Martian robots. There are no other observable differences between this world and our world. Notably, in the alternate world, “cat” is also defined to be an animal in their language. They use the word “cat” just as we do to describe their robot pets. Scientists similarly use the word "cat" when conducting biology on these creatures.

Before I continue, I will explain some terminology. First, reference is the relationship between a word and its subject matter. For example, the word “Aristotle” refers to the man Aristotle. To discuss the word itself, we mention it by surrounding it with quotation marks. Next, “cat” is a so-called natural-kind common noun. Just as proper nouns name particular objects, natural-kind common nouns name groups of objects. In particular, these groups, known as natural kinds, are special. They correspond to groups of objects sharing an underlying nature or governed by natural laws. Some examples of natural-kind common nouns are water, lemons, tigers, and cats.

The thought experiment challenges whether our definitions of natural kind terms are justified by sense experience. Namely, must we go out into the world to confirm that “cats are animals” is true? Or can we justify that statement just by pondering over the meanings of the words? The answer to this hinges on the theory of reference for natural kind terms. This is what is at stake in the thought experiment.

When we describe the alternate world, it may be tempting to say that cats are robots. But even in that world, cats are not robots. (I am using the word “cat” as it is used in the English language.) We are asking if cats—the subject matter—are robots. I think we all agree that cats are animals and certainly not robots. By this reasoning, there are no such cats on the alternate Earth. Cat-like robots are clearly not cats. In fact, we have already stipulated as part of our experiment that there are no cats.

The story is different, however, for someone speaking in the alternate world. Let's say Alice is someone in the alternate world. I argue that in Alice's idiolect, “cats are robots” expresses a truth. Suppose her friend were to respond in his idiolect, “But cats don't exist.” Alice would have a right to object. She might respond: “No, my cat is right there.” And she would be right. Her use of the word “cat” refers to her cat-like robot. It does not refer to cats, of which there are none. Consider when “cat” was introduced to the language hundreds of years ago. It must have been via direct interaction with the robots. Later generations adopted the term “cat” from existing speakers in the community. This is known as a causal connection. Therefore, the weight of usage of “cat” is heavily biased toward referring to robots. Weight of usage measures the degree of influence that speakers have on a word’s usage. Linguistically, it seems problematic if most uses of “cat” fail to refer. From another perspective, suppose scientists in the alternate world later discover the truth about these robots. Putnam argues, I think correctly, that people would continue to refer to the robots as “cats.” People would no longer, however, describe the robots as “animals.”

There is a natural concern regarding the people in the alternate world. Namely, their definition “Cats are animals with such and such characteristics” is wrong. Could it be that when they say “cats,” they still refer to cats? I argue that this mismatch of definition is irrelevant, using the example of whales. The definition for whales was once: “Whales are large fish with such and such characteristics.” Today we know whales are mammals. But suppose we read a manuscript describing whales, written before they were determined to be mammals. This manuscript resembles Alice’s idiolect, particularly in its use of the word “whale.” We would not consider “whale” in the manuscript to mean something different than it does now. Upon discovery, scientists didn’t conclude that what they called “whales” never in fact existed. Rather, they learned that these same whales, contrary to their beliefs, were mammals and not fish. Likewise, suppose the manuscript states, “Whales are fish.” That is a false sentence. It doesn’t matter that it corresponded to the definition at the time. Conversely, a line in the manuscript stating “Whales are mammals” would be true. Again, it is irrelevant that the writer would not have believed that statement. In the same way, “Cats are robots” is a true statement when uttered by Alice.

I further address whether Alice’s term “cat” could refer to both the animals and robots. Let’s modify the thought experiment to include cats. Suppose that there are some cats in the alternate world among the robots. Then Putnam argues that their term “cat” refers only to the true cats. I don’t think this is controversial. They would be mistaken in calling their pets “cats.” Once they find out, they would be keen to label the robots “fake cats.” The difference between these two, I argue, is whether the people are mistaken in their definition. In the original thought experiment, the people really are mistaken. In our modified version, it seems that they aren’t mistaken. This is corroborated by the way each group proceeds upon discovering the robots. We conclude that as soon as there are genuine cats, “cat” refers to them and only them. Thus, it seems that the referent of “cats” depends on the facts of the world.

Let's turn our attention back to our definition of “cat.” Suppose our definition is: “Cats are animals with such and such characteristics.” This definition is clearly true, and we have plenty of justification for it. Cats exhibit all the biological characteristics of animals and have a well-understood evolutionary history. Note that our definition remains true even though we could be greatly deceived. For example, we might be in a situation like the one described in our thought experiment. Indeed, while we should believe our definition is true, we are merely prima facie justified. Our justification here—as with most beliefs—is defeasible. That is, we may encounter future evidence that could overturn our existing justification. But this possibility doesn’t mean our current definition isn’t true.

It may also be tempting to say this sentence can be justified by reason alone. That is, it would be true a priori. A belief is a priori when its justification does not depend on sense experience. For example, “2 + 3 = 5” is true a priori. I don’t need my senses to justify this; reason alone is sufficient. Note that justification is distinct from acquisition, the latter of which always requires sensing. That is, as a matter of basic psychology, acquiring any knowledge requires sensing. But our grounds for justification need not appeal to sense experience. In some cases, definitions are true a priori. Take, for instance, “Bachelors are unmarried men.” This is a priori since bachelors are merely a conventional category, not a natural kind. But cats are a natural kind, so our definition of “cats” must additionally correspond to reality. Take the similar sentence “Water is H2O.” While this sentence is true, it is true as a matter of chemistry. That is, it was discovered empirically, and not given as a matter of definition. Correspondingly, we had to verify that cats are animals with such and such characteristics.

To conclude, our definition cannot be a priori—natural kinds are discovered, not stipulated.