At numerous points during my reading of Thomas Metzinger's new book "The Ego Tunnel" I have come across writing that seems such a crisp description of core ideas (as well as being directly relevant to my own experience) that I want to try to condense and pass the material on to you. I found the following mix of summary, paraphrase, and quotes from chapter 2 to be a calming antidote to my implicit and constant "I can understand this" temperament. (By the way, I first bought this book for my Kindle but then found that the kind of jumping back and around, checking references, that I want to do in reading such a book was impossible, so I purchased the hard copy.) Here's a chunk on the ineffability problem:
In between 430 and 650 nanometers, we can discriminate (make same/different judgements about) more than 150 different wavelengths, or different subjective shades of color. But, if asked to reidentify single colors with a high degree of accuracy, we can do so for fewer than 15. The same is true for other sensory experiences. We can discriminate about 1,400 steps of pitch difference across the audible frequency range, but we can recognize these steps as examples of only about 80 different pitches... Thus we are much better at discriminating perceptual values than we are at identifying or recognizing them.
Metzinger uses a simplest example of two similar shades of green to spell through the consequences of this situation (he calls them Green No. 24 and Green No. 25, nearest possible neighbors on the color chart, such that there's no shade of green between them that you could discriminate). We can experience their difference, but are unable consciously to represent the sameness of Green No. 25 over time. We do not possess introspective identity criteria for this simplest state of consciousness, and we can not pinpoint a minimally sufficient neural correlate of Green No. 25 in the brain if we can not correctly identify the phenomenal aspect of Green No. 25 over time, in repeated trials in a controlled experimental setting. This is why it may be impossible to do what most hard scientists in consciousness research would like to do: show that Green No. 25 is identical with a state in your head.
These simple findings show that there is a depth in pure perception that cannot be grasped or invaded by thought or language. This ineffability problem arises for the simplest forms of sensory awareness, for the finest nuances of sight and touch, of smell and taste, and for those aspect of conscious hearing that underlie the magic and beauty of a musical experience. It almost certainly appears also for empathy, for emotional and intrinsically embodied forms of communication.