The ability to metaphorically project meaning from one sphere of experience to another is a very powerful tool that we human beings have. If it were merely a weak tool allowing us to make simple analogies but did not give us a real purchase on things we find important, it would not matter so much. But it has a very strong functional use.

As cognitive science slowly moves from symbolic to embodied approaches, we still don’t understand the basic problem that metaphors are solving in some way. Where is it that concepts get the structure allowing them to map between more abstract things and less abstract things? We can even start by asking something much more basic: How is it that concepts are able to refer to the world at all? How is it that when I say “cup,” I mean cup? The utterance “cup,” is just a sound. How is it that a sound ever gets to a thing? Experientially a sound has an auditory dimension, and maybe it has a meaning dimension, but an object “cup” doesn’t have any of these. This cup before me is green; it has a handle; it has shape; it has sides; it has location. The word “cup” doesn’t have any of these. So how is it that something with geometric specificity gets labeled by something which has absolutely no geometric capacity at all?

The same kind of problem exists with the myriad abstract concepts which make up our world of psychology and social relationships. So much of our conceptual world has no shape or size or any physical structure, but somehow we are able to use physical language metaphorically to great effect. The deep question has to do with understanding the underlying structures allowing us to take these very different kinds of things and put them together. I think this capacity lies at the very heart of cognition. The chief factor of our intelligence has to do with taking things that are very different from each other and putting them together. For example, the auditory system receives an input which is very different from a visual system. And yet when we perceive the world we map it into this coherent whole with both auditory and visual characteristics. This is the binding problem. How is it that an object, when we see it, has color, shape, size, all of them in the same location, even though the inputs into the system are very different things? Color is not like shape at all.

Another big problem with concepts is that they turn out to be very hard to define. What, for example, really is a “cup”? Is it just something that contains other things? No, because what is contained? Fluids? Yes, but not exclusively. Is a cup something that has a handle? Not necessarily. If I took the handle off this cup, you would still say it’s a cup. Is a cup something that has a handle and is of a certain size, but allows you to be able to drink? Maybe. But if you made a cup big enough for a person who was a giant, 20 feet tall, that would still be a cup for them, while for a child you’d need a cup much smaller. You can go through any concept you want, and it turns out that you just cannot nail it down precisely. Precise, mathematical specificity is something scientists want, but is of little interest to human beings in their normal discourse.

Now is the time to bring in the Buddhist perspective. Nagarguna and other Buddhist philosophers have put forward a deconstructive and interdependent analysis of concepts. They have said all along that concepts cannot be seen as independent and isolated, and thus they cannot be fully characterized. Concepts are useful to us precisely because they interact with other concepts. They’re fluid, metaphorical, and projectible, not something independent of their functional, human, or organismic perspective. This is a perspective that I think even an evolutionary biologist would accept. It also gives us a useful possible hypothesis, which is that concepts are empty. This is a term that can be applied not only in the classic Buddhist sense, but also perhaps as a contribution to a possible modern theory of concepts that formalizes what emptiness means in the realm of cognitive science.

To put it another way, the central capacity we have, which is manifested as metaphors when we use language, is the ability to take two very different domains and map them onto each other. It is the structure of mappings itself that we need to concentrate on, not the various domains. The best way to understand concepts, in other words, is not to individually understand concepts of law, concepts of physics, concepts of chemistry, concepts of emotion, and then study what they are all about. Rather it is our ability to link these concepts together that is important. I believe there can actually be a formalizable, scientific theory of those mappings, by which I mean specifying a relationship between two very different domains. For example, we can map the relationships between words and objects, or between concepts of psychology and concepts of physics. This ability to map into each other two very different things is, I think, at the heart of the cognitive enterprise. Furthermore, emptiness, in a precise technical sense, is a fundamental insight into the nature of these mappings, of concepts in one domain to concepts in another domain.