I often realize that I've had a headache for a while and had not noticed it. It has real effects - I'm feeling grumpy, I'm not being productive - but it's been filtered out before my conscious brain noticed it. I think it's unreasonable to say that I didn't have a headache, just because my conscious brain didn't notice it, when the unconscious parts of my brain very much did notice it.
After a split-brain surgery, patients can experience someone on one side of their body and not notice it with the portion of the brain that is controlling speaking, that is, the portion that seems conscious, but the other portion of the brain still experiences the sensation and reacts to it in a way that can seem inexplicable to the conscious portion of the brain (though the conscious brain will try to make up some sort of explanation for it).
The brain is not unitary, and it is so un-unitary that it seems like a mistake to even act as if subjective experience is a single reality.
The question "did you have a headache when you weren't noticing it?" is the same sort of question as "does an unheard falling tree make a sound?", or, for that matter, "is a wreck of a car up on blocks that will never be driven again still a car?" The error is not specific to the issue of subjectivity.
There's room for nuance here. You can have a sensation without noticing, if it is at the edge of attention. The question in my mind, is the extent to which pain requires attention. I see two ways in which pain involves attention: passively - it can force itself on your attention - and actively - you can be grappling with it in some way.
I am reminded of an anecdote from Celia Green. One day, she thought she had figured out that the essence of pain is the violation of will. A sensation is painful if you don't want it there and can't drive it away. Therefore, she reasoned that if you don't fight the sensation, it will lose its painful valence. She then had an opportunity to test this theory during a trip to the dentist. She was to have a tooth removed, and persuaded the dentist to not use anesthetic.
According to her own account, by embracing what was happening, she was able to neutralize the pain, and the sensations became simply sensations, varying in certain ways but not intrinsically painful. But she hastened to add that this experiment required elaborate psychological preparation in advance, and would not recommend it to the unprepared person.
I think this was recounted in her book Advice to Clever Children.
Interesting: I've had the same thought and did the same experiment, though it wasn't a tooth removal, but some tooth-drilling that I was assured would not be touching a nerve. The normal anesthesia would have been local Novocaine, and I hate how Novocaine feels for the rest of the day. (So it was a choice between two sensations, over two different time periods.) Without the Novocaine, it was like a distant, dull pounding, like falling on a bone, which can be managed. I did this more than once, but my current dentist argued more strongly against it and I acquiesced rather easily.
The main thing I was worried about was controlling my body—I didn't want to flail and disrupt the dentist.
Just like you (and Celia Green) said about the preparation involved, I'd make a distinction between unexpected pain and expected-and-prepared-for pain. You can affect how you feel about a dentist visit, but not a sudden, stabbing pain in the back. (That may be a System-1, System-2 thing.) I've also found that I can relax into something cold—sitting on a stone in winter—but not something hot—being near a fire. We can choose to modify our will about some things, but others are too low-level and force themselves upon us from below.
(Which is part of the topic of "mind breaks down into smaller pieces" that I'm thinking about.)
They're similar-sounding questions, but different.
I think they're very similar. The primary question is 'how do you operationally define {"have a headache"'|"make a sound"}'? The only conundrum is by changing definitions midway through.
Your second example of what it COULD be about is downstream of what it is actually about, but is ALSO the same (if you define "headache" analogously to "sound"), about the limits of induction and measurement.
Your third is still about definitions, including the definition of identity.
I have tinnitus every time I think about the question of whether I have tinnitus. So do I have tinnitus all the time, or only the times when I notice?
From Daniel Ingram's Mastering the Core Teachings of the Buddha (slatestarcodex review):
Immediately after a physical sensation arises and passes is a discrete pulse of reality that is the mental knowing of that physical sensation, here referred to as “mental consciousness” (as contrasted with the problematic concept of “awareness” in Part Five). By physical sensations I mean the five senses of seeing, hearing, smelling, tasting, and touching, and I guess you could add some proprioceptive, other extended sensate abilities and perhaps a few others, but for traditional purposes, let's stick to these five. This habit of creating a mental impression following any of the physical sensations is the standard way the mind operates on phenomena that are no longer actually there, even mental sensations such as seemingly auditory thoughts, that is, mental talk (our inner “voice”), intentions, and mental images. It is like an echo, a resonance. The mind forms a general impression of the object, and that is what we can think about, remember, and process. Then there may be a thought or an image that arises and passes, and then, if the mind is stable, another physical pulse.
Wow! That looks like a great book. Although one can find out by following the links you provided, I'd like to tell everyone here that the book is available for free on the author's website (PDF, epub, mobi).
Yesterday at 9am, I had a headache. I tried to put it out of mind and focus on other things, and I guess I was successful because the next time I thought about it, it was 10am and I didn't have a headache. (I'm simplifying and making up times that are approximately right.)
So it went away, but when did it go away? Did it end at 9:10am and I just didn't notice until 50 minutes later, or did it end at 9:50am? In physics-speak, it was an unobserved variable between the two measurements.
Taking the word "head-ache" literally, I didn't have a headache at all from 9:01am through 9:59am because I wasn't noticing it, not perceiving it, and therefore not feeling it. A "pain" that you don't feel is not pain. How can it make sense to say, "This hurts but I can't feel it"?
If I noticed I had a headache at 8am and I noticed I had a headache at 9am and the physical mechanism causing it didn't change over that interval, but I wasn't noticing it, did I really have a headache from 8:01am through 8:59am?
Suppose that the physical mechanism can be detected by an fMRI machine, and I was being monitored all morning. A neuroscientist could point to an angry blob on the computer screen and say, "There's your headache. It definitely existed from 7:30am until 9:30am, when the aspirin kicked in. Whether you were aware of it or paying attention to it is another matter."
The headache that the neuroscientist is talking about is a different thing from the "head-ache" that I'm talking about. In fact, all of our words about sense perceptions and thoughts are doubled like this: my sense of taste is one thing, chemical interactions on my tongue are another, my feeling of excitement is one thing, adrenaline in my blood is another, and my feeling that I understand a mathematical concept is distinct from my ability to answer questions about it[1]. Sure, they're highly correlated, but that doesn't make them identical. If your measurements of all the objective criteria disagree with my assertions of my subjective experiences, you might wonder if I'm lying or don't understand the common usage of the words, but they're not 100% guaranteed to go hand-in-hand.
This is an elaboration on Reality #5 in my previous essay on Reality and reality-boxes. My point is that the physical reality of chemical interactions on my tongue, adrenaline in my blood, and my quiz results on a mathematical concept are not all there is to say about taste, excitement, or understanding—they're not the same things as my experience of taste, excitement, and understanding, and they're not better than/truer than my subjective experiences of these things. They're qualitatively different.
In that essay, I included a parable of a physicist and a neuroscientist, in which the physicist took her status as a rational being as a starting point to perform experiments and develop the physics of fMRI machines, and the neuroscientist used the fMRI machine to find the neural correlates of her thinking that she's a rational being. It would be odd to say that the fMRI reveals a deeper reality, that consciousness and subjective experience is an illusion while physical measurements are real, since it's our use of consciousness and subjective experience that undergirds and interprets those physical measurements. Not only are they different, but each one swallows the other like some sort of ouroboros.
Subjective reality is an odd sort of reality. Perhaps the neural correlate of my headache existed from 7:30am to 9:30am, but if I only asked myself, "Do I have a headache?" at 8am, 9am, and 10am, then the subjective head-ache could only exist at those times when I was thinking about it. Suppose a part of my mind is thinking about it, which doesn't occupy the central spotlight of my attention—does that count? The "me" in this subjective experience seems to break down into partial-mes, some of which are content to stay subconscious while others are vying for attention. Perhaps the oddest thing about subjective reality is our inability to communicate it: I know that I have subjective experiences, but I only assume that you do because I'm not a sopalist. But then, if parts of my consciousness can be broken down into subsystems, would those parts have the same kind of skepticism about each other that I have about you?
I'm struggling to write a longer essay on how consciousness is made of pieces of not-quite-conscious thought-stuff below the level of subjective experience, and that it's also a part of not-quite-conscious thought-stuff above the level of subjective experience as well, that human society is a loosely connected, incoherently thinking brain. But even though it can be broken down into pieces, I don't want to lose sight of the fact that subjective experience is a primary reality—we couldn't even approach the other realities without it.
An example may help: when I finished my first course in thermodynamics, I could pass the tests but didn't feel like I knew what the subject was about. It's so different from other branches of physics that I didn't feel like I had a handle on it. So I took a long walk in order to think about it, and by the end of that walk, I felt like I had a better understanding by categorizing thermodynamics more as a kind of math than as a kind of physics. My ability to solve problems on tests didn't change: by objective measures, my newfound feeling of insight was rather useless, but it seemed more important to me than my test-taking ability.
I recognized something similar when I met a mathematician who believed he "didn't really understand the Pythagorean Theorem." Obviously, he could solve problems about it, but he felt there was something bigger in it that he wasn't grasping—maybe something that nobody has grasped yet. If he ever did end up satisfying that itch, chances are that he wouldn't be able to communicate it directly. Maybe he could introduce a few new theorems or connections with other fields, but whether those theorems fill the hole (and whether there's a hole in the first place) may be something that happens differently in each individual mathematician.