• Michael Ossipoff
    966
    Where is the fact? It is simply a proposal (hence the proposition). — Rich


    Rich added:
    Rich
    Because you say so? Suppose sometime disagrees?

    I replied:

    If you doubt that premise, that doesn't mean that you disagree with or challenge the if-then proposition.

    Rich answered:

    I just did.

    I didn't mean you couldn't disagree. Obviously you can disagree with anything that you want to. I merely meant that you can't validly, justifiably disagree with an if-then proposition based on a belief that its premise is false.

    To get an idea regarding what you're talking about, i recommend that you re-read the post that you're "replying" to.

    The falsity of an implication proposition's premise doesn't make the impiication-proposition false. In fact, by the standard 2-valued truth-functional definition of an implication, the falsity of an implication's premise makes the premise true.

    But, even if you don't like that standard definition, the falsity of an implication's premise certainly doesn't make the implication false.

    You're repeating your previous comments, without paying attention to the answer that was given.

    Finding "facts" outside of philosophy class is actually quite difficult.

    Facts aren't at all difficult to find.

    You call yourself "Rich". That's a fact. Maybe "Rich" is really your first name. That, too, is a fact.

    Those are just 2 examples. There are many other uncontroversial facts.

    Establishing the premises of implications might be difficult. For example, regarding the if-then facts on which my metaphysics is based, many or most of their premises may very well be false, because I don't make any claims about anything being real or existent.

    (In fact, because "real" and "existent" are metaphysically undefined, any claim that something is or isn't "real" or "existent" is a claim using meaningless words.)

    That in no way invalidates the if-then facts.

    But your statement quoted above seems based on a misunderstanding of what "fact" means. You're probably just expressing, in another way, your suspicion about the truth of the premises of some if-then facts. I've answered that.

    Michael Ossipoff
  • Rich
    3.1k
    I merely meant that you can't validly, justifiably disagree with an if-then proposition based on a belief that its premise is false.Michael Ossipoff

    Of course I can.

    The falsity of an implication's premise doesn't make the proposition false.Michael Ossipoff

    IF there is disagreement with the premise THEN there will be disagreement with the conclusion (as there always is). One might as well forget about everything until there is concensus with the premise/stated belief. I would think this is pretty obvious.

    But, even if you don't like that standard definition, the falsity of an implication's premise certainly doesn't make the implication false.Michael Ossipoff

    Yes, when people agree, they will agree. It is not true or false, it is the nature of human beings. Agreement (consensus) is often restated as facts. Despite this, it remains a belief.

    You call yourself "Rich". That's a fact. Maybe "Rich" is really your first name. That, too, is a fact.Michael Ossipoff

    No one knows what Rich is. You can say something about it and I might agree, but suppose I'm a hacker and have nothing to do with the name Rich? All information is subject to ambiguity some more so than others. You form beliefs but it doesn't make it a fact.

    The problem with most analysis of the nature of things is that people are in need such a hurry to reach conclusions that they don't even pause for a second to consider alternatives that would undermined their conclusions. This is no doubt a product of an educational system that encourages the idea of "pat answers". That is why I stopped going to college courses. It trains students that there are facts that can be spoon fed by higher authorities. Actually those are the worst sources for information.
  • Michael Ossipoff
    966


    You need to do more (or at least some) listening, and less expounding.
    .
    I’d said:
    .
    I merely meant that you can't validly, justifiably disagree with an if-then proposition based on a belief that its premise is false.
    .
    You replied:
    .
    Of course I can.
    .
    I didn’t say you couldn’t disagree. I merely said that you couldn’t validly and justifiably disagree.
    .
    …because the truth of an if-then proposition doesn’t at all depend on the truth of its premise.
    .
    (…except that, by the 2-valued truth-functional definition of implication, the falsity of an implication’s premise makes that implication true by definition.)
    .
    Here’s a tip: Find out something about a subject before you expound on it.
    .
    Yes, saying that to you is a waste of time.
    .
    I’d said:
    .
    The falsity of an implication's premise doesn't make the proposition false.
    .
    You reply:
    .
    IF there is disagreement with the premise THEN there will be disagreement with the conclusion
    .
    First you confuse the implication with its premise. Now you confuse it with its conclusion
    .
    So yes, if you disagree with an implication-proposition’ s premise then you can (but needn’t) also disagree with its conclusion.
    .
    The falsity of both the premise and conclusion of an implication-proposition doesn’t imply the falsity of the implication-premise.
    .
    In fact, by the standard 2-valued truth-functional definition of an implication-proposition, if is premise is false, and its conclusion is false, then the implication-proposition is (by definition) true.
    .
    But, even if you don’t like that definition, the falsity of both the premise and the conclusion of an implication-proposition certainly doesn’t contradict that implication-proposition.
    .
    As I said before, if an implication’s premise is false, then the implication is saying nothing whatsoever about the truth of its conclusion.
    .
    Your belief in the falsity of an implication-proposition’s premise and/or conclusion in no way implies a belief in the falsity of the implication-proposition itself.
    .
    You need to get it straight, regarding the difference between an implication-proposition, its premise and its conclusion.
    .
    …or at least you need to get that straight before expounding about the subject.
    .
    IF there is disagreement with the premise THEN there will be disagreement with the conclusion (as there always is)
    .
    Actually no. If I believe that an implication’s premise is true, and you believe that its premise is false, then we could both agree that its conclusion is true. …even if we both believe that the implication itself is true (…and even if we both agree that the implication itself is false…and even if we disagree on whether the implication is true or false.).
    .
    Remember that an implication whose premise is false says nothing whatsoever about the truth of its conclusion.
    .
    . One might as well forget about everything until there is concensus with the premise/stated belief. I would think this is pretty obvious.
    .
    …pretty obvious to you, and entirely wrong.
    .
    Yes, if we don’t know if an implication’s premise is true, then (even if we assume that the implication itself is true), we don’t know if its conclusion is true.
    .
    But not knowing if an implication’s premise is true doesn’t mean that we don’t know if the implication-proposition itself is true.
    .
    Some implication-propositions can be shown to be timelessly true, without testing them by looking at their conclusion in every instance. Some would just be agreed by all to be true, without argument.
    .
    For example, my metaphysics is about abstract if-then facts, and I don’t claim that all of their premises are true, or claim anything about the “reality” or “existence” (whatever that would mean) of the abstract facts or what they refer to.
    .
    What if it can be shown by argument, or it’s otherwise agreed, that an implication-proposition is intrinsically, inevitably, timelessly true?
    .
    Unless someone shows an instance of its premise being true and its conclusion being false, there’s no reason to doubt that demonstration or agreement. (…unless someone shows an error in the demonstration.)
    .
    I’d said:
    .
    But, even if you don't like that standard definition, the falsity of an implication's premise certainly doesn't make the implication false.
    .
    You replied:
    .
    Yes, when people agree, they will agree. It is not true or false, it is the nature of human beings. Agreement (consensus) is often restated as facts. Despite this, it remains a belief.
    .
    …none of which has any bearing on this topic.
    .
    And, contrary to what you seem to mean, there really are facts. But we’ve been over that.
    .
    I’d said:
    .
    You call yourself "Rich". That's a fact. Maybe "Rich" is really your first name. That, too, is a fact.
    .
    You answered:
    .
    No one knows what Rich is. You can say something about it and I might agree, but suppose I'm a hacker and have nothing to do with the name Rich?
    .
    Irrelevant. You call yourself “Rich”. As I said, that’s a fact.
    .
    All information is subject to ambiguity some more so than others.
    .
    No, you call yourself “Rich”, by using it as your login-name, and signing your posts with “Rich”. That isn’t subject to ambiguity.
    .
    Maybe each “Rich” post is really from a different person. Fine. Right now you’re signing your post “Rich”. Thereby, you un-ambiguously calling yourself “Rich”.
    .
    If all dogs are mammals, and all mammals are animals, then all dogs are animals.
    .
    That’s another fact that isn’t subject to ambiguity.
    .
    You form beliefs but it doesn't make it a fact.
    .
    I never said that all of your beliefs are facts.
    .
    The problem with most analysis of the nature of things is that people are in need such a hurry to reach conclusions that they don't even pause for a second to consider alternatives that would undermined their conclusions.
    .
    Exactly! That’s why you’ve got to check your conclusions before you post.
    .
    Michael Ossipoff
  • Rich
    3.1k
    .
    I didn’t say you couldn’t disagree. I merely said that you couldn’t validly and justifiably disagree.
    Michael Ossipoff

    What makes you think you didn't understand your declaration of final arbiter? I did. I fully understand that you believe you are in the position of greater understanding. Fine. I disagree.

    If you want to argue about what is valid and what is true and all of those other arbitrary terms, there is a thread thrashing that out right now. Suffice to say, I don't recognize you as the final arbiter. That belief is your own.

    You called me Rich. I never called myself anything. Check your facts.
  • Michael Ossipoff
    966
    What makes you think you didn't understand your declaration of final arbiter? I did. I fully understand that you believe you are in the position of greater understanding. Fine. I disagree.Rich

    And that's what your problem is: Your delusional belief in your understanding of a topic on which you're quite clueless.

    Is this about fuzzy relativism?

    You're so innocent of any exposure to the subject, that you think that the things I've told you are just one person's personal opinion.

    It's alright do disagree. But it would be better to disagree after educating yourself on the subject a bit.

    If you want to argue about what is valid and what is true and all of those other arbitrary terms, there is a thread thrashing that out right now.

    Actually, there's much in logic about which there's widespread and firm consensus.

    Sorry, but it's not a subject for Rich to make up.

    My message to you is just that you should educate yourself, at least a little, before you post.

    Suffice to say, I don't recognize you as the final arbiter. That belief is your own.

    As I said, I'm not the final arbiter. But you're befuddled, all confused about the differences between an implication, its premise, and its conclusion.

    Though I'm not the final arbiter, you need to educate yourself, at least a little, before you expound.

    You called me Rich. I never called myself anything. Check your facts.

    You're using "Rich" as your log-in name.

    I've wasted enough time replying to vain, delusional ignorance.

    My participation in this conversation is concluded.

    Michael Ossipoff
  • Rich
    3.1k
    Your delusional beliefMichael Ossipoff

    May I return the favor, which was my original point, but I believe I said it far more eloquently.
  • TheMadFool
    2k
    As for myself, I just keep it real by observing patterns, understanding human nature, always working on sharpening my skills via "cross-training", and like any good detective, making sure all the pieces in the puzzle are fitting together. Philosophy is all about being a good detective whose working to solve the case. I like challenges that thoroughly test my capabilities and creative thinking possibilities. It takes time to develop the skills but it is never too early or late to startRich

    But doubt casts a shadow over everything - your assumptions AND your methods. It's great to think of philosophy as an investigation but what if our technique is wrong or our clues are faulty? What then?

    Of course I may be charged of asking for a ridiculous amount of certainty. However, who decides on what degree of certainty is acceptable?

    Let's first look at method viz. Logic/rationality. To evaluate rationality we use rationality itself. In other words we already assume rationality is the correct method when we put rationality under the lens. It's a vicious circle.

    I've had discussions with others and some have said that to examine rationality with rationality isn't a vicious circle as it appears. Rationality vindicates itself through ways other than itself. For instance it makes predictions which are accurate. It works over a wide range of fields from children's lego blocks to advanced chemistry and physics. Therefore, one can say that rationality has universal application over space and time - rationality has proven itself.

    That's why I've used logic to make the argument in my OP.

    Come to assumptions and we don't have that degree of certainty as we had for rationality. We can't be sure of our assumptions. In fact philosophical arguments seem to be exactly about differing assumptions. The method - rationality - is universal but the premises/assumptions are not.

    So, given the situation it seems we can't be sure of finding truths in the sense of indubitable ones that withstand any and all rational assaults. This is the problem I'm talking about. We can doubt ALL truths and still be completely rational.

    Being a good detective requires one to continually assess our own assumptions and methods, right?
  • Rich
    3.1k
    But doubt casts a shadow over everything - your assumptions AND your methods. It's great to think of philosophy as an investigation but what if our technique is wrong or our clues are faulty? What then?TheMadFool

    I change direction. I'm only interested in understanding nature. The more I look the better my skills.

    The problem with logic is that you never go beyond where you are and the only skill that you are honing is restatement of what you already know. If you want to enhance your skills in life you have to go out there and experiment and do it. I don't look for certainty. I look for knowledge that allows me to grow.
  • TheMadFool
    2k
    Of course there are truths.Michael Ossipoff

    I just proved it. Can you name one truth that you're 100% sure of?

    Maybe the problem is the notion of "absolute certainty", not scepticismYing

    But then this solution leads to arbitrariness - something that isn't rational, right? We come to a consensus on what degree of certainty is acceptable but that decision is arbitrary. Anyway, I'm with you on this one. I think radical doubt should be used instead of solved. Every time we think we've found something we should doubt its veracity.


    We become sceptics and attain ataraxia. It's not particularly hard.Ying

    Skeptical ataraxia. Ok
  • TheMadFool
    2k
    I change direction. I'm only interested in understanding nature. The more I look the better my skills.

    The problem with logic is that you never go beyond where you are and the only skill that you are honing is restatement if what you already know. If you want to enhance your skills in life you have to go out there and experiment and do it. I don't look for certainty. I look for knowledge that allows me to grow.
    Rich

    That's a very pragmatic and beautiful.

    As I said in my reply to Ying, radical doubt should be used rather than solved because as a tool it serves to remind ourselves to check and recheck our beliefs and as a problem it's unsolvable.
  • Rich
    3.1k
    As I said in my reply to Ying, radical doubt should be used rather than solved because as a tool it serves to remind ourselves to check and recheck our beliefs and as a problem it's unsolvable.TheMadFool

    Yes, doubt pushes us forward to discover more. We are all explorers.
  • gurugeorge
    165
    Do any of you have any idea what that/those truth(s) is/are?TheMadFool

    Well the cogito is a pretty good candidate for indubitable truth, but the trouble is it doesn't necessarily connect to any other truths, it leaves you in a position where you have to preface every claim with "it seems to me that ..." - but of course we want to know whether is, not just seems.

    As others have said, the process of doubt is usually limited, it depends on prior acceptance of some truth(s). To doubt, you need some truths as a lever. If you extend doubt infinitely, then you automatically limit yourself to the cogito, in fact to strict solipsism, and you stay there so long as you're infinitely extending your doubt.

    So that said, the "indubitable" truths that we work with on a day-to-day basis are mostly simple, perceptual level truths, truths that are based on the animal level of perception that your ancestors used to survive and pass on their genes with. That's not a guarantee of absolute certainty, and they're always subject to correction, but they're the closest things we have to absolute certainty in the empirical realm.

    I think a lot of it (particularly with Descartes methodology) is a confusion between the processes of ordinary knowledge-gathering and the processes of mathematical/logical thinking.

    In ordinary knowledge-gathering, you're actually making discoveries, you're learning something new about the world, new information. But this has to mean that empirical knowledge is always provisional.

    In maths and logic, on the other hand, with a complex or difficult problem, you feel subjectively like you're making a discovery, like you would in the everyday process of knowledge-gathering, but what you're discovering was already implicit in the axioms, etc., that you start out with, so you're not in fact discovering new information, just unfolding what was implicit. (It may be new information to you, but that novelty is strictly subjective.)

    What this means is that the standard of certainty in maths and logic cannot be applied to empirical knowledge, except in the sense that in empirical knowledge-gathering, you are creating an internally-consistent projection or model of how the world is, that you then test against eventuating reality. There's mathematical certainty, deductive certainty, within the model and the implications for testing that you can draw from it. But you can never be certain that the model you're using is the right model for the occasion.

    And that's where empirical doubt is always possible, and it's basically the putting side-by-side of two internally consistent models. IOW, an anomaly crops up in experience, which means that there must be something wrong with the model you've been assuming to be true up till now; so then you figure out some other possible model for the world, and match your two models against each other, and filter the right one out on the basis of homely, perceptual level truths (measurements, meter readings, etc.) that you are less doubtful about.
  • Michael Ossipoff
    966
    Of course there are truths.Michael Ossipoff

    Can you name one truth that you're 100% sure of?TheMadFool

    I'll name two:

    1. If all dogs are mammals, and all mammals are animals, then all dogs are animals.

    2, A posting attributed to Mad Fool asked me, " Can you name one truth that you're 100% sure of?"

    Michael Ossipoff
  • TheMadFool
    2k
    Well, radical doubt will question the certainty with which you assert truths. Are you sure it's not a demon manipulating your mind?
  • TheMadFool
    2k
    Sorry I flagged your comment by mistake. Some changes since I last visited the site. Sorry again.

    Anyway, thanks for your reply. I learned a lot from it.
  • Michael Ossipoff
    966
    Well, radical doubt will question the certainty with which you assert truths. Are you sure it's not a demon manipulating your mind?TheMadFool

    Then you believe in demons. I don't share that belief of yours.

    Aside from that, are you referring to the doubt, or the asserted certainty?

    Asserted certainty:

    I do claim that there are uncontroversial metaphysical statements.

    ...but I don't make as many assertions as you might think, because I make no claim that the complex system of inter-referring timeless abstract if-then facts about hypotheticals, that i refer to, is "real" or "existent". (...whatever those words would mean.)

    Doubt:

    How sure are you that words can accurately and completely describe all of Reality?

    If you can't say for sure that that's true, then any claim about all of Reality is questionable.

    In any case, I'm not interested in debating or convincing anyone about the limits of discussion or description. I'd rather just discuss metaphysics, which is agreed, by most, to be discussable.

    Michael Ossipoff
  • TheMadFool
    2k
    If you can't say for sure that that's true, then any claim about all of Reality is questionable.Michael Ossipoff

    That's what I mean. Radical doubt is, must be, painful to philosophers because it undermines everything, from their axioms to their logic.
  • PossibleAaran
    105
    I should say my piece in favour of Descartes' method.

    I think it's right to say that Descartes was looking for indubitable truths to serve as foundations from which he could infer anything else he was going to believe. He begins the search by considering his cognitions in general and, in particular, his sensory experiences. He tries to locate cognitions that are self-certifying. An explication of "self-certifying" is best found by illustration. Consider the practice of gazing into a crystal ball in order to contact the dead. The gazer comes to form various beliefs about what the dead are saying. It is possible to ask why we should take what the gazer says at all seriously. Why should we think that what he says is true? He will likely retreat back to the claim that his crystal ball allows him to contact the dead, but we will immediately wonder why we should take this at all seriously. Why should we think that his crystal ball is reliable about these things? If we cannot find any answer to that question, there is a sense in which we will fail to assure ourselves that what the gazer says is true. That is, there will be a "why" question which he simply cannot answer.

    All of these same issues arise for any and every method of belief formation. For example, I might answer a why question about my belief that there is a laptop in front of me by saying that I can see one, but this will lead to the question of why I should take sense perception to be reliable. I read Descartes as noticing this fact, that someone who is genuinely curious about the truth of their beliefs in general will raise why questions about any and every such belief. He seeks a way out of it - to satisfy his curiosity about the truth of his beliefs. To that end, he looks for beliefs about which a further why question makes no sense. He then tries to build the rest of his philosophy on top of those beliefs. His criterion for foundations ends up being clarity and distinctness. He thinks that when something is, in some sense, clear and distinct, there is no further question it makes sense to ask about why it should be accepted. He also thought that propositions that were clear and distinct were absolutely certain, but we should note that whether or not clear and distinct propositions are such that no further why question makes sense about them, and whether or not they are absolutely certain are logically two completely different matters.

    Many people think something like the following about Descartes. Descartes is lead into solipsism because he requires absolute certainty for his beliefs. If you don't require absolute certainty, then you can escape and believe everything that you normally do. Doubt is thus just a silly game of demanding certainty when it isn't needed. It is true that Descartes pursues absolute certainty in the Meditations. His foundations are absolutely certain, and he insists only on deductive inference which would preserve certainty. But it isn't true that just by abandoning that standard you can avoid the issues Descartes gets himself into. Suppose that we relax the standard of certainty to probability. We could then, in principle, allow merely probable foundations and probable inferences. We are still limited, however, to propositions such that no further why question makes sense. Philosophers who have relaxed the standard seem to me to have failed far worse than Descartes ever did. They either fail to recognize that intelligible "why" questions can still be raised about their foundations or they simply don't see the regress of why questions; they only see certainty, and dismiss Descartes for being obsessed with certainty.

    From this perspective, consider Gurugeorge's Model Building ideas:

    you are creating an internally-consistent projection or model of how the world is, that you then test against eventuating reality. There's mathematical certainty, deductive certainty, within the model and the implications for testing that you can draw from it. But you can never be certain that the model you're using is the right model for the occasion.gurugeorge

    How does a model get "tested against reality"?

    an anomaly crops up in experience, which means that there must be something wrong with the model you've been assuming to be true up till now; so then you figure out some other possible model for the world, and match your two models against each other, and filter the right one out on the basis of homely, perceptual level truths (measurements, meter readings, etc.) that you are less doubtful about.gurugeorge

    These ideas obviously assume that sense perception is reliable, and it is painfully easy to ask, why think that sense perception is reliable? And Gurugeorge seemingly has no answer to this question. The model building idea strikes me as very similar to Falsificationism, and I am attracted to that doctrine, but it has to be propped up by the claim that sensory experiences yield beliefs about which no further why question can be raised, and (since deduction is needed to deduce that a model is false given certain experiences) the claim that the rules of deductive inference have that status too. There may be ways to make these claims stick, but to do so one would have to employ either Descartes' idea of clarity and distinctness, or something which does the same job of answering that final why question. But those who say that Descartes' was just obsessed with certainty (perhaps guru doesn't hold this), never give such accounts. This is why I think they fail even more than Descartes did.

    Now, it might be that part of the model we are building is the assumption that sense perception and deduction are reliable, but if it is, what sense does it make to say that the model itself is tested by appeal to sense experience? To test a model which contains the theory that sense perception and deduction are reliable by appeal to sense perception and deduction is clearly question begging. Thus, these ideas about models always leave one with an unanswered "why" question about the key assumptions of the model. It isn't just that the assumptions aren't absolutely certain. Its worse than that. Its that no reason at all has been given to think the assumptions are true, not even a fallible or probable one.

    Hence, construed as an attempt to solve the problem Descartes tried to solve, the model building ideas are a failure. If, however, the model building ideas aren't an attempted solution to that problem, I admit that I have no real idea how to understand them.

    I should apologize to for picking on his post as an illustration. I wanted some way to make the Cartesian perspective clear by contrasting it with some other ideas. His post was the most well thought out and lucid of those that seemed appropriate for this purpose.

    Best
    PA
  • gurugeorge
    165
    and it is painfully easy to ask, why think that sense perception is reliable?PossibleAaran

    Great post! All I'll say here is that this is the nub of it: the only reason one gets so much as the idea that there's an anomaly (that casts doubt on one's model) in the first place, is because one is already relying on sense perception as valid enough to tell you that there's an anomaly; therefore, unless one is given reason to suppose otherwise, the subsequent model-testing sense-perceptions can have at least the same level of reliability. (And the "reasons to suppose otherwise" usually involve some break in the conditions for normal perception, with the possibility of correcting perception being already priorly accepted.)

    IOW, if you think there's an anomaly at all, that information comes to you from sense perception, therefore (unless there's good reason to suppose otherwise - that's where the burden of proof lies) whatever perceptions you use to test your revised conception of reality must be on exactly the same level of reliability as the perceptions that gave you the very idea that there was an anomaly in the first place. The more certain you are that there was an anomaly, the more certain you must be that sense perception is at least in principle reliable enough to resolve the anomaly.

    Going back to the arguments from illusion (and the gradual progression of Cartesian doubts in the course of the Meditations): the only reason why you think you were subject to an illusion (or why Descartes noticed he'd been in error about various things) is because of some corrective perception that reveals that your previous perception was an illusion. Therefore you're already implicitly allowing the validity of at least some sense perceptions: the corrective sense perceptions at least must be valid, for the illusion to be genuinely an illusion. Therefore you can't use the argument from illusion to globally doubt the validity of sense perception on the basis that sometimes you're subject to illusion.
  • PossibleAaran
    105
    the only reason why you think you were subject to an illusion (or why Descartes noticed he'd been in error about various things) is because of some corrective perception that reveals that your previous perception was an illusion. Therefore you're already implicitly allowing the validity of at least some sense perceptions: the corrective sense perceptions at least must be valid, for the illusion to be genuinely an illusion. Therefore you can't use the argument from illusion to globally doubt the validity of sense perception on the basis that sometimes you're subject to illusion.gurugeorge

    Thanks for the reply guru. It seems we are slowly isolating the key disagreements between us. Here is one of them. You think that what Descartes does is something like this. He first notices that he has sometimes been mistaken. From this fact he extrapolates that he might be mistaken in any given instance, and that is why he suspends judgement prior to finding his proof of God's existence and such. If this were how he was thinking, then I'd say you would be right that to get this started, he has to take fore-granted that at least some of his sensory experiences are veridical. It seems right to me to say that he can't really do that unless he is already assuming the reliability of sense perception, and so that assumption would be a presupposition of the possibility of his doubting it. A remarkable transcendental argument against scepticism!

    My reply would be that even if Descartes did proceed in the way you think, he need not have done so. Descartes need not assume that sometimes he is mistaken, in order to ask "why believe that sense perception is reliable?". He can simply ask it, can he not? Of course, he cannot sensibly ask it if he is also assuming that sense perception is never mistaken or if he is assuming that sense perception is reliable. But he need not assume that. He can simply raise, relentlessly, with respect to every opinion he has, "why believe that?", until he reaches some beliefs for which this question cannot meaningfully be posed.

    But, given your initial remarks about "getting the idea that there is an anomaly" in one's model, perhaps you think that for some reason Descartes cannot sensibly raise this question about the reliability of sense perception. It would be great if that were so, but how could it be?

    Best
    PA
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