I haven’t thought much about the application of the idea ‘skepticism’ since the first year of my philosophy program, because it had already been sorted out to my satisfaction and the satisfaction of my instructors.

Someone mentioned it in a comment, and I’m wondering about its relevance. To me it’s applicable to every philosophical discourse as an implicit presumption; weak skeptisism it's part of the grounding for contemporary intellection.

Here’s the crux of the problem as described by Duncan Pritchard in the IEP. The sections bracketed by quotation marks are Pritchard's quotes from Nagel, T. (1986). The View from Nowhere, Oxford University Press, Oxford, England:

We realise that the initial appearances present to a viewpoint can be unreliable guides to reality and therefore seek to modify our ‘subjective' view with a more ‘objective’ perspective that is tempered by reason and reflection. As Nagel points out, however, the trouble with this approach is that

"[...] if initial appearances are not in themselves reliable guides to reality, [then] why should the products of detached reflection be any different? Why aren't they [...] equally doubtful [...]? [...] The same ideas that make the pursuit of objectivity seem necessary for knowledge make both objectivity and knowledge seem, on reflection, unattainable." (Nagel 1986, 76)

We can reconstruct the argument here as follows. We recognise that our initial unmodified ‘subjective' experience of the world is unreliable and therefore should be adapted along ‘objective’ lines by eliminating the ‘subjective’ element. For instance, initial appearances tell us, falsely, that straight sticks suddenly become ‘bent’ when placed in water. Accordingly, we modify our initial ‘subjective’ view with the testimony of ‘objective’ scientific investigation which tells us that the stick in fact stays straight, it is just the light that is bending. However, and here is the crux of the matter as far as Nagel is concerned, why do we regard this modified view as being any more reliable than the completely ‘subjective’ perspective that it replaces? After all, we cannot eliminate every trace of ‘subjectivity’ and thus the problematic component of our conception of reality that engendered the pursuit of objectivity in the first place remains. Consequently, we are both aware of the need for objectivity whilst also recognising that such objectivity is impossible. As a result, according to Nagel, we are condemned to the following pessimistic evaluation of our epistemic capacities:

"The search for objective knowledge, because of its commitment to a realist picture, is inescapably subject to skepticism and cannot refute it but must proceed under its shadow. [...] Skepticism [...] is a problem only because of the realist claims of objectivity." (Nagel 1986, 71)

That is, the problem of skepticism [...] "has no solution, but to recognise that is to come as near as we can to living in the light of truth (Nagel 1986, 231)."

Here’s what I learned in philosophy school; it’s worked for me ever since:

A) Strong skepticism: (“There is no knowledge” or “There is no true knowledge”) is self-refuting thus incoherent. Also, it’s impossible to prove that something doesn’t exist (see Proving Non-Existence).

B) Weak Skepticism 1: We can’t possibly verify that we’ve inferred anything for certain about anything that we can’t observe directly. This is Kant’s insight that our linguistic theories and models of unobservable things can’t ever be verified by comparison with those (supposed)things. This realisation deflated correspondence theory and triggered a new age of philosophy.

C) Weak skepticism 2: Popper eventually capitulated to the postmodern wave which swept Europe after Kant’s intervention when he admitted that only knowledge in the symbolic (formal) languages of logic and arithmetic is certainly true. “All else [including] the natural sciences … is essentially conjectural … there simply are no sufficient reasons for holding those hypotheses to be true, let alone certainly true.” (Objective Knowledge: an Evolutionary Approach, p. 75)

To me weak skeptisism is applicable to every philosophical discourse as an implicit presumption; it's part of the grounding for contemporary intellection.

Is skepticism an issue for anybody here? Is there any question or contention about it around here?

  • A simple period of reflection may not improve on ones initial subjective conclusion. What makes scientific objective thought different from simple conntemplation is that it produces ideas which can be tested. Ideas which predict. Ideas which can be built upon. For example scientific inquiry into refraction produced eyeglasses, and microscopes, which then allowed us to discover bacteria, which led us to cure disease etc. Scientific skepticism is undeniably uncontentious.
    – Richard
    Apr 14, 2019 at 22:41
  • Your "strong skepticism" is more of a straw man, careful radical skepticism (doubting that any knowledge is possible) is not self-refuting, although highly suspect on pragmatic grounds. Universal methodological skepticism (Cartesian doubt) predates Kant, and holds a place of pride in modern philosophy, but its utility also has been questioned, see How far can/should one press philosophical doubt? See also IEP's Contemporary Skepticism and SEP's Skepticism.
    – Conifold
    Apr 14, 2019 at 23:29
  • @Conifold.."skepticism (doubting that any knowledge is possible) is not self-refuting"...Hmmm. Is subjective belief a type of knowledge? A feeling? Linguistic lore? These are definitively available to us. Are they possible? Why think otherwise? Does 'knowledge' only refer to a conception (and its related conceptions, no idea stands alone) that's indubitable?..."utility also has been questioned"...Well, yeah, it's notoriously difficult to calculate!...Does that imply that it's not desirable, an abstract value that's not worth its pragmatic weight?
    – Rortian
    Apr 15, 2019 at 1:03
  • 1
    What I, or other users, think is for forums, not a Q&A site like SE.
    – Conifold
    Apr 15, 2019 at 17:44
  • 1
    @PeterJ, I understand that you believe that you know the truth about philosophy, and I sympathise with this view, even though it defies my experience and contradicts the acclaimed experts on the leading edge of the field for the past century. I asked you many reasonable questions and you haven’t offered any justification other than your insistence that your beliefs must be true. I learned in my first philosophy class that philosophy these days is about inquiry, not certainty. That includes considering other perspectives and their justifications, so I continue to inquire.
    – Rortian
    Apr 18, 2019 at 21:01

2 Answers 2


You are correct that strong skepticism is self-refuting and thus invalid. Weak skepticism 1/2 also refute themselves since philosophers observe the world through their senses and thus any logical framework they build is contingent on their ability to perceive the world and to assume the world remains such after the philosopher looks away. Example: A = A has to be inferred after the initial observation else it needs to be checked over and over again indefinitely for any implications of A = A to be valid under weak skepticism.

Personally, skepticism is not an issue since logic, like science, is valid until it is refuted. The only thing we can say about any argument is that it has not been invalidated yet. In fact, it is impossible to validate any logical argument since doing so requires logic outside the argument, which makes that logic not validated, etc. It's why tautologies are not actual logical fallacies. C = A, because A = B and B = C.

If you want a simple heuristic though, anything denying the validity of science (a trillion dollar industry that has resulted in human supremacy) is probably not valid and even if it was, subscribing to such a system would quickly lead to your demise and thus your not-subscribing to said science-denying system. Simply, it's impossible to stay subscribed to skepticism forever.


I completely disagree: strong skepticism isn't self refuting in an interesting way. The strong skeptic can say that they know one thing, or are they just engaged in the psychological gratification to 'everything'? Though I guess it may be "incoherent" in a less semantic sense.

Your breakdown of different skepticisms is interesting, and makes intuitive (coherent) sense. Many, if not all, Marxists would not want to ally Popper so closely to analytic certainty and a lack of empirical certainty. It just seems unlikely to them that "psuedo-sciences" like Marxism consist of no true conjecture at all.

  • What about "I suppose that total certainty is unwarranted"...Popper wasn't dumb enough to say he knows that he can't know, he was aware that we're conjecturing. "I know that I don't know" is true if it's false and false if it's true! Is that an "opinion"?! lol
    – Rortian
    Apr 17, 2019 at 0:35
  • that's appealing @Rortian
    – user38026
    Apr 17, 2019 at 0:37
  • but i can't see what you're disagreeing with (apologies for that). i don't think i'm expressing an opinion, even if the first two paragraphs have no substantial basis in any literature i've read @Rortian i fixed what i was saying ('true' / 'certain' etc.), apologies for my mistake
    – user38026
    Apr 17, 2019 at 0:45
  • it was just an issue of clarity (invalid wasn't meant in the technical sense) @Rortian anyway
    – user38026
    Apr 17, 2019 at 0:53
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    thanks, @another_name.
    – Rortian
    Apr 17, 2019 at 0:55

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