- The Enigma of Perception by D.L.C. Maclachlan
In this interesting, clear, and well-written book, D.L.C. Maclachlan, a distinguished philosopher of perception at Queen’s University, seeks to rehabilitate a traditional theory of perceptual knowledge—that it is inferred from “the sensations external things produce in us.” The problem, as Maclachlan explains, is that such inference has to rely on prior knowledge of external causation. I experience an auditory sensation. This is an event that is internal to my consciousness. How can I infer from this that somebody is speaking? To do so requires that I already know that people produce such sensations in me by speaking. But this “prior knowledge” [End Page 339] is of precisely the kind that tradition claims is inferred from sensation. Thus, the tradition pushes us into a circle from which there is no exit.
Maclachlan’s solution is to distinguish two ways of “conceptualizing” sense experience. In one way of looking at it, it is just as the tradition has it, a simple effect of the external world. In another, it engages what Immanuel Kant calls “the faculty of representation.” Taken in this second way, sense experience is how external things appear to a “standard subject,” by virtue of how the human perceptual system is constructed. Take the auditory sensation again. From Maclachlan’s perspective, it has this other aspect—it is a representation of somebody speaking.
Does this solve the problem? Not yet, says Maclachlan: “We are still lacking the acid test—the check against reality … [T]here is still no way to check sense experiences against the reality that transcends them.” To this he responds that sense experiences in one modality and experiences of acting can be used to structure our concepts of things in the world beyond subjective experience. The difficulty is that this construction is credible only if one presupposes that there is such a world. But, as he says, this presupposition can be minimal. It need not commit us to any particular ontology of objects. “The purely formal concept of reality built into our response to the sensory input leaves completely indeterminate the reality that is the object of cognition.” All we need is the assumption that there is something unstructured out there, and that there is space and time, and then we can impose our structure on it.
There is a good bit more detail in Maclachlan’s picture, though it is not possible to present his ideas critically in a short review. One question I would ask of him is why he thinks that sense perception offers so little by way of concepts of the external world. Why is it necessary for us to provide the structure? As he is well aware, there is a long tradition of psychologists and philosophers—ranging from René Descartes to the Gestalt psychologists—who hold that the perceptual image is as such of a world that contains discrete material objects. Maclachlan dismisses this notion in a way that strikes this reviewer as doctrinaire.
When they are theorizing about perception, it is to philosophers’ advantage to dip into a variety of sources, including scientific studies of the perceptual process. To his credit, Maclachlan gives scientific findings a go, but he is not always sure-footed. To give a representative example, he discusses—with a single citation from the New York Times—blindsight, the much studied phenomenon of individuals who, as a result of cortical lesions, are capable of visually guided movement, even though they lack conscious visual experience. He says that this “establishes conclusively” that there is perceptual knowledge that is not inferred from sensation. In fact, this is wrong; blindsighted patients know how to navigate the environment, but they do not do this by deploying descriptive knowledge. They lack perceptual knowledge of any truth, the traditional domain of [End Page 340] inferred knowledge. In this and other places in the book, one wishes for a more empirically nuanced approach.
The Enigma of Perception is a fine book that presents a powerful connected argument that carries...