The past two nights I fell asleep thinking about the difference between real sense data and imagined sense data. There is a world of difference between seeing the color red and imagining the color red. I don’t know why this hadn’t occurred to me before, but the distinction is remarkable.

I thought about memories. What are the actual properties of memory? The more I thought about it, the more elusive these properties became. If I close my eyes and recall a particularly vivid memory, I find now that I am at a loss to describe what it is I am actually experiencing (right now). It isn’t visual. It is not as if I am watching “with my mind’s eye” a movie clip of the memory. There are no tactical sensations in my body. A particular memory from childhood that is distinct becomes a third-person description of an event. It can’t have been experienced this way.

Memory recall of this kind seems most analogous to visual sense experience, but the analogy breaks down upon close inspection. There is nothing mysterious to me about the fact that we have memory. What is mysterious is the phenomenon of recalling memories, or re-experiencing them.

Buddhist teaching identifies six senses. There are the usual five senses by which we experience the outside world plus one for introspection. Perhaps meditation intensifies the strangeness of this “sixth sense.”