The buddhists have a fairly well worked out description of 6 senses, which are (oddly) the 5 familiar in the West: sight, hearing, touch, smell, and taste, and a sixth, which is thought.

First off, note that the familiar five provide a bad description of the sensory component of our being. Smell and taste are not separate. Touch is not one, but a whole host, of senses, including heat, vibration, pain and gentle touch, and then there’s all the proprioceptive and vestibular stuff. OK. But to Western eyes, the notion of thought as a sense is a bit peculiar. We actually don’t have a good account of what thought is, so this is interesting. How do we make sense of thought as a sixth sense?

Most notions of sense are predicated upon a split between organism and world. But everything we know about consciousness assures us that the domain of present phenomenal experience arises from the embeddedness of an organism in a world, without a dualistic, causal split between these two co-defining things.

In psychophysics, there is an old distinction between prothetic and metathetic features of a stimulus, or a sensory channel. Consider sound. Some features of sound are of the “how much” variety. Loudness, for example. Sound can be overly loud. But frequency of a pitched sound is not of this kind. There, the discriminations we make are of the “what kind and where” type. A note cannot be unbearably high pitched in the same way that it can be unbearably loud. The “too much” features are prothetic (brightness is another such), the “what kind” features are metathetic (color or hue belongs here).

If we reject the inner/outer distinction, and acknowledge the difficulty in trying to force a divide between subject and world, then much of thought appears as a primarily metathetic modality specific way of bringing forth a world, not really different from many aspects of vision or audition. Perhaps we should talk to the Buddhists.