A good place to begin understanding why consciousness is not strictly reducible to the material is in looking at consciousness of material objects — that is, straightforward perception. Perception as it is experienced by human beings is the explicit sense of being aware of something material other than oneself. Consider your awareness of a glass sitting on a table near you. Light reflects from the glass, enters your eyes, and triggers activity in your visual pathways. The standard neuroscientific account says that your perception of the glass is the result of, or just is, this neural activity. There is a chain of causes and effects connecting the glass with the neural activity in your brain that is entirely compatible with, as in Dennett’s words, “the same physical principles, laws, and raw materials that suffice” to explain everything else in the material universe.
Unfortunately for neuroscientism, the inward causal path explains how the light gets into your brain but not how it results in a gaze that looks out. The inward causal path does not deliver your awareness of the glass as an item explicitly separate from you — as over there with respect to yourself, who is over here. This aspect of consciousness is known as intentionality (which is not to be confused with intentions). Intentionality designates the way that we are conscious of something, and that the contents of our consciousness are thus about something; and, in the case of human consciousness, that we are conscious of it as something other than ourselves. But there is nothing in the activity of the visual cortex, consisting of nerve impulses that are no more than material events in a material object, which could make that activity be about the things that you see. In other words, in intentionality we have something fundamental about consciousness that is left unexplained by the neurological account.