Two Different Types of Certainty?

[Seeker]

More precisely, the fact that we cannot read minds does not prevent us from having "conclusive" (C2) certainty, but it is a barrier to ever having absolute, 100% (C1) certainty.

Why? What conclusions entail mindreading?

Edited August 6, 2007 by Seeker

[DavidOdden]

Sometimes. All conclusions that are beyond all doubt (C1) are also conclusive (C2), but not the other way around. Some conclusive (C2) conclusions are based on a standard of proof such as "beyond a reasonable doubt," that does not exclude all doubt. In the chain of reasoning that leads up to a such conclusive conclusion there may be unknowns such that the causal chain between perception and conclusion has gaps in it.

Not sometimes, always. If you have moved beyond doubt, are free of doubt, and have no reason to doubt, then that describes being "certain". If there are gaps in the reasoning, the proof is not conclusive, it is "very highly probable". It is utterly wrong for an Objectivist to refer to "very highly probable" as "being certain". Your error arises in confusing the necessity of acting, with certainty. When a man must act, he does so on the basis of the evidence that he has available. It is not necessay to demand certainty -- you simply have to recognise that your decision to act may be founded on a false conclusion, but the best-supported conclusion available to you. Certainty is something different -- it is freedom from doubt.

[ttn]

It doesn't make sense, because the evidentiary continuum is fundamentally about resolving doubt. Once all doubt is resolved, you are at the end and can go no farther.

I don't think that formulation is correct. It suggests that we start with hypothetical conclusions which we entirely doubt, then slowly whittle away our doubt until none remains, at which point we are certain of the conclusion. But the gaining of knowledge is fundamentally the achievement of a positive, not the removal of a negative. What the evidentiary continuum is fundamentally about is simply the fact that certain complex ideas require complex, multi-step validations. The evidence needed to establish the conclusion has to be assembled and organized, piece by piece. The evidentiary continuum designates the various intermediate stages of this development. It is true that, prior to achieving certainty, there are typically some rational empirical grounds for doubt. But to define certainty (and the rest of the continuum) in terms of (amount of remaining) doubt is, I think, to define it in terms of a non-essential.

Certainty is not about the total count of bits of evidence, it's about the proportion of evidence -- 100%.

This is also misleading. Certainty is definitely about both "quantity" and "proportion" (though "total count of bits" isn't quite the right way to describe the "quantity" aspect). As noted previously, it's possible for 100% of the evidence to point toward a certain conclusion, yet for that body of evidence to be insufficient to establish the conclusion, i.e., for that body of evidence to fail to fulfill the relevant standard of proof. Conceptualizing certainty merely in terms of the "proportion of evidence" (without regard to the sufficiency of evidence vis a vis the relevant standard) makes certainty subjective, and would lead, in practice, to systematic premature claims to certainty -- i.e., systematically finding oneself in the position of having claimed certainty about things that turn out to be wrong.

[dan_edge]

I tried tackling this issue a few years ago in a paper for my Senior Seminar in Philosophy class: Objectivism and the Correspondence Theory of Truth. I'm sure there are many things I would change if I wrote the paper again, but it could serve as good food for thought, particularly regarding how one could be certain, then turn out being wrong.

--Dan Edge

[DavidOdden]

I don't think that formulation is correct. It suggests that we start with hypothetical conclusions which we entirely doubt, then slowly whittle away our doubt until none remains, at which point we are certain of the conclusion.

It does not suggest that. In fact, an Objectivist epistemology dictates that you not start that way, because arbitrary propositions are antithetical to man's method of cognition. You start with some perceptual fact that you become aware of, and seek to integrate that fact into your knowledge. Thus you already start with a conclusion that has some support, and the process of integrating that knowledge causes you to distinguish your preferred hypothesis from alternatives. The competing hypotheses predict different things, and doubt arises (must arise) when you do not know which things are actually facts, by gaining knowledge of those facts (such as the terperature of the solution after 1 minute). Because of the law of the excluded middle, adding positive knowledge means eliminating competing theories. Furthermore, if you have two competing theories that are well-supported and which make partially identical predictions in a context, adding confirming evidence in that context is useless because it doesn't distinguish the competing theories.

What the evidentiary continuum is fundamentally about is simply the fact that certain complex ideas require complex, multi-step validations.

I don't know what you mean by that, but as I understand what you said, that is incorrect. Again, I recommend re-reading Peikoff's discussion of the progression from "possible" through "probably" to "certain". The clearest refutation of the "complex, multi-step validation" theory is direct perception itself. A simple way to convince yourself of that is to stick a needle into your finger, and see whether a complex, multi-step validation is required to be certain as to what happened.

This is also misleading. Certainty is definitely about both "quantity" and "proportion" (though "total count of bits" isn't quite the right way to describe the "quantity" aspect). As noted previously, it's possible for 100% of the evidence to point toward a certain conclusion, yet for that body of evidence to be insufficient to establish the conclusion, i.e., for that body of evidence to fail to fulfill the relevant standard of proof.

This is untrue, and you will need to concretize that in the form of an example. The notion of "sufficiency of evidence" is destructive of a rational epistemology. When you articulate what "sufficient evidence" would be, and what the standard of sufficiency is, I think you will find that it means "sufficient to dispel existing doubts that arise from your existing knowledge", and thus the "100% of the evidence" account that Peikoff gives subsusmes the notion of "sufficiency of evidence". (Of course, if you have some different notion of what "sufficient evidence" is, when you explain that notion, I can show you how it is already covered by Peikoff's account).

Conceptualizing certainty merely in terms of the "proportion of evidence" (without regard to the sufficiency of evidence vis a vis the relevant standard) makes certainty subjective, and would lead, in practice, to systematic premature claims to certainty -- i.e., systematically finding oneself in the position of having claimed certainty about things that turn out to be wrong.

I don't see how that is possible. If you are referring to erroneous claims of certainty, it's always possible for a person to declare their feeling of certainty about a conclusion, even if the feeling isn't based in a proper validation. That's why Peikoff discusses the topic in terms of the proposition being certain, not the person feeling certain about the proposition.

[ttn]

It does not suggest that. [....]

I have the sense that discussing this further (to the point of coming to agreement) would be a major undertaking that I don't have time for. So I will let my previous statements stand without further elaboration, and simply register that I strongly but respectfully disagree with much of what was said in David's post -- and in particular with the assertion that my views are "destructive of a rational epistemology".

I would, however, second David's suggestion that interested people might benefit from a careful study of OPAR.

[DavidOdden]

I strongly but respectfully disagree with much of what was said in David's post -- and in particular with the assertion that my views are "destructive of a rational epistemology".

You did not understand what I said -- I said that it is the notion of "sufficiency of evidence" that is destructive of a rational epistemology. It's unfortunate if you don't feel that you can explain the basis for your claim, but that's your prerogative. I agree that these discussions do take a lot of time.

[ttn]

You did not understand what I said -- I said that it is the notion of "sufficiency of evidence" that is destructive of a rational epistemology. It's unfortunate if you don't feel that you can explain the basis for your claim, but that's your prerogative. I agree that these discussions do take a lot of time.

I think I understood what you wrote just fine. The notion (of the importance, vis a vis "certainty") of "sufficiency of evidence" was the primary view I spoke in favor of. So what you said is indeed that my views are destructive...

But forget it. The reason I don't want to discuss this further is emphatically not that I'm "personally affronted" by what you said. You obviously didn't intend the comments personally, and I didn't take them that way. The reason is just that there are many, many confusions (and contortions of Objectivism) in your post, which, it is clear to me, would take a long long time to identify and unravel. And I don't have time for that kind of discussion.

Again, just to be clear: the reason I quoted your bit about "destructive to rational epistemology" was not to accuse you of accusing me of something. I hate it when people initiate -- or escalate -- this kind of "you were irrationally rude in accusing me of X" nonsense in these discussions. Discussions of this kind almost always center around disagreements, and there needn't be anything personal or insulting about this. (Incidentally, here is a point -- perhaps the only one in many many years -- where I agree with Betsy about something: many of the remarks made on her website in criticism of LP's infamous comments about the last big election were perfectly reasonable expressions of disagreement with certain aspects of those comments. I find very dubious the people who go out of their way to interpret these as "vicious attacks" and thereby convert a discussion of ideas into pressure group warfare about who "dissed" whom.) So please don't get me wrong. I'm not at all annoyed or offended, nor do I feel like you dissed me, nor do I want anybody to step in and argue that I should be treated with more respect, etc., etc. (I have way more respect for people who are willing to say what they think, even when it involves open disagreement, but who remain open to improved understanding via further debate/discussion.) And hopefully you will feel the same way when I say: instead, the reason I don't want to discuss it further is that I think you badly misunderstand certain core aspects of Objectivist epistemology, and that will make any subsequent discussion too involved and too long.

[DavidOdden]

I hate it when people initiate -- or escalate -- this kind of "you were irrationally rude in accusing me of X" nonsense in these discussions.

I agree entirely. Few things irritate me more than intellectual cowards hiding behind an excuse, such as "you were rude, I heneceforth shun thee", when they mean "I have no argument".

[MisterSwig]

[T]he evidentiary continuum is fundamentally about resolving doubt. Once all doubt is resolved, you are at the end and can go no farther.

This is where we differ. I think that the evidentiary continuum is fundamentally about gathering evidence for a conclusion. The removal of doubt and the achievement of certainty (about a conclusion) are effects of the gathering of evidence (and the use of reason).

We would not say that life is fundamentally about resolving unhappiness, would we? Life is about achieving values, which then makes us happy. Similarly, the evidentiary continuum is not fundamentally about resolving doubt. It is about finding facts, i.e., gathering evidence. Removing doubt and unhappiness is merely a consequence of gaining facts and values.

Edited August 6, 2007 by MisterSwig

[Seeker]

The evidentiary continuum is fundamentally about achieving certainty (in the cognitive, not emotional sense). Your doubts are the road map that tell you what evidence you need to gather.

Do you agree with David's explanation that the continuum is closed-ended, i.e. a matter of proportion?

Edited August 6, 2007 by Seeker

[DavidOdden]

It is about finding facts, i.e., gathering evidence.

This is where we fundamentally disagree. Gathering evidence is not the goal, it is a means of reaching a goal. The goal is having a conceptual grasp of reality, of being able to distinguish the true from the false on a principled basis. But maybe it would help to expand on what this doubt stuff is about. The alternative is not "This conclusion, or ignorance" -- that's the Popperian line (and for a Popperian, it's always "ignorance"). The alternative is "This conclusion, or that". If you are seeking to validate a conclusion as being certain, there is (or should be) a concrete alternative, and the doubt is "which of these two conclusions is the correct one". If you cannot eliminate B as an alternative explanation, then you do not know that A is correct.

[MisterSwig]

The evidentiary continuum is fundamentally about achieving certainty (in the cognitive, not emotional sense). Your doubts are the road map that tell you what evidence you need to gather.

I think that the "road map" is the standard of proof, not one's doubts. When I doubt a conclusion, it is because I have not reached the standard of proof.

I could sit around and doubt my girlfriend's honesty all day long, but that won't tell me what sort of evidence I need in order to form a valid conclusion about her moral character. For that I need to identify some kind of standard of proof that needs to be reached. Only in relation to a standard of proof can I know what sort of evidence is relevant to my conclusion. Thus, the thing that guides me in my evidence-gathering is my standard, not my doubt.

Do you agree with David's explanation that the continuum is closed-ended, i.e. a matter of proportion?

I'm not sure I understand this idea of "proportion" with regard to the continuum of evidence. I need to think about David's position some more, before I respond to it.

[Seeker]

I could sit around and doubt my girlfriend's honesty all day long

I take that to be asserting that I am claiming that doubts are arbitrary. That is false. All alternative hypotheses must have at least some evidence to support them or we wouldn't be considering them in the first place. If you did have a reason to doubt your girlfriend's honesty, then instead of sitting around you would be investigating to discover evidence of what the facts of reality are so as to rule out one of the alternatives (that she is honest, or that she is dishonest), so that you could then know (i.e. be certain of) which hypothesis is correct.

[MisterSwig]

I take that to be asserting that I am claiming that doubts are arbitrary. That is false. All alternative hypotheses must have at least some evidence to support them or we wouldn't be considering them in the first place. If you did have a reason to doubt your girlfriend's honesty, then instead of sitting around you would be investigating to discover evidence of what the facts of reality are so as to rule out one of the alternatives (that she is honest, or that she is dishonest), so that you could then know (i.e. be certain of) which hypothesis is correct.

In my example, my girlfriend can be honest or dishonest. But that doesn't mean that I have two hypotheses: one, that she is honest, and two, that she is dishonest, both with evidence supporting them. Until I gather some evidence that points in either direction, I am ignorant of her moral character.

Let's say I have some evidence to support the hypothesis that she is honest. I can still be in doubt regarding that hypothesis, if I have not reached the standard of proof necessary to conclude that she is in fact honest. Such doubt, however, is not based on any evidence for her being dishonest. It is based on the fact that I have not reached the standard of proof required to conclude that she is honest. I'm still ignorant of her moral character, but it is looking like she is honest.

I did not mean to imply that you believe doubts are arbitrary. I was challenging the idea that one's doubts are a "road map that tells you what evidence you need to gather."

Edited August 7, 2007 by MisterSwig

[Seeker]

In my example, my girlfriend can be honest or dishonest. But that doesn't mean that I have two hypotheses: one, that she is honest, and two, that she is dishonest, both with evidence supporting them. Until I gather some evidence that points in either direction, I am ignorant of her moral character.

Well then, doubting your girlfriend's honesty all day long is perfectly appropriate. I had taken your example to mean that her honesty was already known and thus my arbitrary doubts were groundless. But thank you for clarifying your example. Still, whatever reasons you have to doubt serve to guide your efforts to gather the evidence you need, so I am not sure where the disagreement lies in regards to that. My main point is that once you know something (i.e. are certain of it), you cannot know it more with greater evidence.

[DavidOdden]

I'm not sure I understand this idea of "proportion" with regard to the continuum of evidence.

It's not anything fancy. If no evidence supports the proposition, the claim is arbitrary -- 0 (no) support. If 100% of the evidence points to the conclusion, the claim is certain. Between 0% and 100% there is a continuum of degrees of evidence, and perhaps when 60% of the evidence support the claim we would say that the claim is "probable". When 100% of the evidence support the conclusion and you add new evidence that also and unsurprisingly supports the conclusion, you still have the same proportion -- 100% -- even though you have have more evidence.

I could sit around and doubt my girlfriend's honesty all day long, but that won't tell me what sort of evidence I need in order to form a valid conclusion about her moral character.

In an epistemology allowing only the integration of perceptually-gained fact using logic, you can't "just doubt", you have to doubt based on some fact. Start by naming that fact -- if you can't name it, then the doubt is arbitrary.

In my example, my girlfriend can be honest or dishonest. But that doesn't mean that I have two hypotheses: one, that she is honest, and two, that she is dishonest, both with evidence supporting them. Until I gather some evidence that points in either direction, I am ignorant of her moral character.

This is mildly odd: it seems to me that for her to be a girlfriend, you had better have evidence regarding her moral character. With a complete stranger, it's more plausible to be ignorant as to moral character, but not with a girlfriend. I mean, assuming you've signed on to the Objectivist account of love, and not the Hot Chick theory.

What exactly is the standard of proof regarding honesty that you seek -- how do you arrive at / discover / objectively justify that standard? Let me propose an alternative question, not about moral character, just to clear up the question about standard of proof. A mammal is a warm-blooded vertebrate with hair and sweat glands some of which produce milk (and other stuff no doubt). If you discover an animal and find repeated and overwhelming evidence that it is warm-blooded and vertebrate, but you have no further evidence about the animal, the essential characteristics necessary to validate the conclusion are not in evidence. Two of them are, and you don't have any evidence supporting an alternative (such as scales, feathers or gills), but as far as the essential distinguishing characteristics go, you can at best conclude that the animal is a bird or mammal, so you can't make a specific refinement of your conclusion to the particular choice "mammal" based on your knowledge. This, it seems to me, is the proper role for the notion of "standard of proof" -- identification of the essential characteristics which distinguish one conclusion from another.

Perhaps if you reexamine the evidence regarding your girlfriend, you will realise that the doubt arises because you don't have the evidence to establish whether she is thoroughly honest, or honest on most counts but evasive on occasion. (It's a subtle distinction, but there is a difference between being downright crooked and being a low-key reality-evader). That could explain why she canceled her last two dental appointments for no apparent reason -- personally, I hate the noise of the drill, and maybe she's evading that, possibly without full awareness of what she's doing.

[Seeker]

In my example, my girlfriend can be honest or dishonest. But that doesn't mean that I have two hypotheses: one, that she is honest, and two, that she is dishonest, both with evidence supporting them.

To be clear, what you have is the fact that there are two alternatives, only one of which is true. The doubt comes in because you don't know the essential fact needed to fulfill the standard of proof by telling you which one it is. The lack of knowing essential distinguishing fact(s) in the context of fulfilling a standard of proof is the grounds for doubt.

To say that 100% of the evidence points in a single direction means that the total of the available evidence leaves no room for doubt, i.e. fulfills the standard of proof. So for example, if you have two murder suspects both of whom had motive and means, but only one of which had opportunity, 100% of the evidence points in a single direction - but that doesn't mean you don't still have the evidence that the other suspect had motive and means. That evidence is still there, and it still points towards the conclusion. What happens is that the conclusion in evidence is refined with each step.

Edited August 7, 2007 by Seeker

[Betsy]

Whatever she says elsewhere, Betsy has not only observed the use of two concepts, but used them herself. She endorses both of them as valid concepts, even when I and others have argued in detail that neither of them are valid.

Yes I do use them both myself and I believe that they are both valid, but different, concepts denoted by the same word. In fact, I looked up "certain*" only the Objectivism CDROM and found Ayn Rand using the term "certainty" in both of the senses I indicated, depending on the context. (In addition, she also used it in a third sense to mean a feeling of confidence in a judgment whether justified or not.)

By the way, if calling attention to the dangerous philosophical implications of someone's words is a "negative personal thing," then I think "poisoning the wells" is a fantastic idea. It just isn't a fallacy!!

The problem isn't "calling attention to the dangerous philosophical implications of someone's words," but claiming something is dangerous one has not proved to be someone's actual position or actually dangerous. Whittaker Chambers asserting that Ayn Rand wanted to send people to the gas chambers does not make it so.

[Betsy]

After reviewing post #82 and post #98 in the other thread, it is clear that Betsy is invoking different standards of proof that, when reached, constitute certainty (that those standards of proof have been met). C2 is Peikoff certainty from OPAR chapter 5. C1 is a special instance of C2 in which the standard of proof is "absolute" such that it is impossible to be proven wrong later. Because of this, it is highly unlikely that Betsy will acknowledge a disagreement with OPAR ch. 5 (other than her preference that "certainty" refer only to certainty in which the standard of proof is "absolute").

You've got it!

What we have then, according to Betsy's approach, is certainty that a conclusion has been validated "absolutely", or certainty that a conclusion has been validated "beyond a reasonable doubt". So I can see now how she is using the OPAR concept of certainty by plugging in different standards of proof,

Yes, but what is an appropriate standard of proof is not arbitrary. It is determined by the nature of the entities you are judging. You judge what makes a rock move differently from what makes a person move.

but then the question simply turns from "degrees of certainty" to standards of proof, and the same objections apply - that there is no distinction between the standards, that all knowledge is contextual, etc.

All knowledge is contextual and the context determines the standard of proof. For example, in civil cases the standard of proof is "the preponderance of evidence" while in criminal cases it is "beyond a reasonable doubt and to a moral certainty."

[Betsy]

I think this passage from OPAR, p. 177, is relevant to this discussion:

I agree with that.

We all recognize that man is capable of being dishonest, but from this fact Betsy invalidly infers that maybe Mr. X is being dishonest, when there are no grounds to suspect that Mr. X exercised his capacity to be dishonest.

That is not my view. My position is that absence of evidence of dishonesty does not prove anything about a person's honesty or dishonesty or the probability thereof. Absence of evidene isn't any kind of evidence one way or another.

You need more evidence of actual virtue to conclude a person is probably virtuous and you may never have enough evidence to conclude that they are virtuous with the same certainty you have about your own virtue.

[Betsy]

What conclusion that doesn't rely upon axiom, sense perception, or a valid, proper causal explanation has a valid role in man's cognition? So far you have cited conclusions involving mens rea, but isn't it true that there are inductive principles by which to validly and with causal explanations, infer such conclusions?

Yes, given enough of the right kind of evidence. Unfortunately, we often have to form conclusions and choose courses of action based on incomplete evidence. In those cases, there are inductive principles we can use to come up with the best conclusion under the circumstances, but such conclusions will never be as certain as when we have all the evidence we need.

Again I think this all comes down to some unspecified, unwarranted doubt you have that is (for you) precluding certainty by a rational standard, hence we are told that we must make do with certainty by an irrational standard.

There is nothing irrational about acknowledging the fact that our conclusions can only be as certain as the available evidence allows.

[Seeker]

All knowledge is contextual and the context determines the standard of proof. For example, in civil cases the standard of proof is "the preponderance of evidence" while in criminal cases it is "beyond a reasonable doubt and to a moral certainty."

While standard of proof can simply mean a place on the evidentiary continuum in some contexts, it clearly means something different in this context. The standard of proof is the distinguishing facts that need to be proven, for instance, that the suspect is the only person who had motive, opportunity, and means (OPAR ch. 5, p. 179).

Yes, given enough of the right kind of evidence.

Thank you for acknowledging that in at least some cases, we can indeed infer mens rea with certainty (not degrees of certainty, not possible or probable or very highly probable, but certainty, such that no doubt remains, the fact-standard of proof has been fully met, there is no higher to go on the evidential continuuum and more evidence won't make us any more certain, not even if we could read minds).

Unfortunately, we often have to form conclusions and choose courses of action based on incomplete evidence. In those cases, there are inductive principles we can use to come up with the best conclusion under the circumstances, but such conclusions will never be as certain as when we have all the evidence we need.

Which is to say, you aren't certain unless you meet your standard of proof. If the evidence fails to show that Mr. X had the requisite intent in the context of a murder trial, then he isn't convicted of murder even if he very highly probably is the culprit. That is one reason why I think it is so important to not misuse the word "certainty" to mean "very highly probable". You don't want to cause the sort of confusion that could result in Mr. X being mistakenly sent to the gallows.

Edited August 7, 2007 by Seeker

[Thomas M. Miovas Jr.]

I'm having some problems with my computer at home, since I keep getting a "can't write to disk" error message, a bunch of noise, then it locks up and crashes; so I'm probably not going to be able to say a lot on this topic until I get a new hard drive and reformat it and so on...to top it off, I tied to log onto oo.net and got an IPS data error message.

At any rate, I don't think that alieviating doubt is the goal of knowledge. Knowledge is understanding existence, which fundamentally means organizing one's observations according to similarities. The problem with the idea that one has two theories and one or the other must be right is that neither one may be right. A given theory may be used as a guide to some investigations, but organizing one's observations (induction versus deduction) according to the facts one knows is the better approach. Alieviating doubt comes across as Descarte's method, and saying it must be one or the other when it comes to competing theories comes across as Plato's method -- i.e. they both come across as rationalism, at least as stated.

Also, saying that one has enough information (and needs no further information) once one reaches the standard of proof comes across as, "Don't confuse me with the facts, my mind is already made up." Obtaining more relevant facts is how one continuously assesses whether or not one was correct. That is why it is possible to be contextually absolutely right, but still be wrong (in light of new evidence).

I think part of the problem in this thread and one reason everyone seems to be talking past one another is that what is being talked about isn't being brought down to simple examples. A lot of people are talking in terms of broad abstractions, and others think they know what is being talked about, but then the original poster says no that isn't what I am talking about. And so it goes.

And I think we need to keep in mind that Objectivism is a new philosophy, and that sometimes this means that we cannot fall back on colloquial usages of terms (such as what "certainty" means in a court of law).

I'll try to reply to some specific posts, but that may have to wait until I get my computer at home back up and running.

[DavidOdden]

At any rate, I don't think that alieviating doubt is the goal of knowledge.

I agree -- eliminating doubt is a method for acquiring knowledge. Until doubt as to alternatives is eliminated, you don't know, you only suspect.

The problem with the idea that one has two theories and one or the other must be right is that neither one may be right.

If you build the theory from the ground up, then I don't see how that is possible, but of course if you short-circuit the process of building knowledge incrementally and skip the logical validation part for foundational ideas, I agree that you can easily be faced with two false theories.

Also, saying that one has enough information (and needs no further information) once one reaches the standard of proof comes across as, "Don't confuse me with the facts, my mind is already made up."

I think it only comes across that way in a culture that denies the possibility of knowledge and reviles the concept of certainty, as we unfortunately live in. The perennially open mind has no real knowledge, because everything is open to reexamination, and thus the simplest of measurements is only an "approximation" and we can't be sure that the water is boiling at 100 C because we're not certain about the thermometer and the science underlying it. If we set aside the skeptic epistemology that we're indoctrinated in and allow that one can indeed have certain knowledge, that there is a difference between knowledge and suspicion and, most importantly, that we can even learn to distinguish things that we know versus things that we suspect by following a rigorous program of validating out knowledge and by constructing knowledge on a foundation of knowledge, not suspicion -- then I don't see any problem with saying that at a certain point we cantually can know something, and that we have completed that particular epistemological task, and can move on the the next one.

I think part of the problem in this thread and one reason everyone seems to be talking past one another is that what is being talked about isn't being brought down to simple examples.

I agree -- realistic, concrete examples are necessary. It's really hard to provide a full logical justification for a conceptual-level statement, but it should be done. Unfortunately, this started with a question about man's consciousness, which IMO is the hardest thing in the world to establish certainty about. Simple physical examples are easier, because we know vastly more about that than about the mind. Still, the principles are applicable to all subject matters -- or would be, if we could agree on the principles.