I was banned from Uncommon Descent this morning for reasons unknown (though here is a plausible hypothesis). At the time of my banning, I was in the midst of a long discussion of absolute certainty and whether it can rationally be claimed. Since I can’t continue the discussion at UD, I’ll start a thread here instead and solicit the opinions of the very smart locals here at TSZ.

The question is whether there we can be absolutely certain of anything. I am not speaking of absolute certainty in the colloquial sense (“I’m absolutely certain I left the keys on the counter!”), but in the precise sense of 100.0% (unrounded) certainty, with literally no possibility at all of error — not even a trillionth of a trillionth of a trillionth of a percent chance of error.

It seems obvious to me that we cannot rationally claim that kind of certainty because we know that our minds are fallible. We know that we can be mistaken without realizing it, even in cases where we *feel* absolutely certain. The example I used at UD was the certainty many 19th-century scientists felt, before Einstein, about the “self-evident” absolute and distinct nature of space and time.

Given the ever-present possibility of error, I think it’s pure hubris to claim absolute certainty of anything – even something as seemingly inescapable as Descartes’ famous *cogito*.

Not surprisingly, the regulars at UD disagreed. Kairosfocus in particular was in hysterics over the supposed dire consequences of my view. What surprised me, though, was that Lizzie also disagreed with me. I am interested in hearing more about why she disagrees, and also in what the rest of you think.

Is absolute certainty possible? If so, what can we be absolutely certain about? What (if anything) justifies absolute certainty? I look forward to your answers.

Lizzielol

And, true.

PatrickBut so potentially beneficial that it’s worth some effort!

petrushkaPerhaps just a dome.

keithsPost authorkairosfocus, at UD:

KF,

Either you misunderstood the professor, or he gave you a bad answer.

You are interpreting “X -> Y” as meaning “if X is true, then Y is true”. That’s what we mean when we say “X implies Y” informally.

In formal logic, however, “X -> Y” is a statement like any other. That means it can be either true or false, depending on the values of X and Y, and X and Y can take on any combination of values.

X and Y also need not have anything to do with each other. Regardless of what X and Y stand for, the value of “X -> Y” can be obtained from the appropriate truth table.

For example, let X stand for “John is a Republican” and let Y stand for “Salmon swim upstream to spawn.” Suppose John really is a Republican, so that X is true. We already know that salmon swim upstream to spawn, so Y is true. Looking at the truth table, we see that if X and Y are both true, then X -> Y is also true. However, that obviously does

notmean that John’s party affiliation determines whether salmon swim upstream to spawn.If you keep this in mind, your confusion over the Socrates syllogism will vanish.

r0bbKeiths:

We should give Stephen credit for finally recognizing a long-standing error of his. From his OP:

He responded to counterexamples by claiming that this applies only if there is a single premise, apparently not realizing that any set of premises A, B, C, … can be restated as a single premise “A and B and C …”, which is false if any of its components is false.

But he later conceded that his belief was mistaken, to which I say Hallelujah.

For years he has failed to recognize the unidirectionality of implication, thinking that a true consequent can only follow from a true antecedent. For example:

And he has long tried to demonstrate the truth of his claims by pointing to a true consequent of each claim. For example:

Now that StephenB seems to have figured out that affirming the consequent is a fallacy, perhaps he’ll rethink some of his previous arguments, along with his condescension toward those whom he lectures about “reason”.

keithsPost authorIf we could arrange for StephenB to bet life or limb on it, I think we’d quickly discover that StephenB is not absolutely certain of his absolute certainties.

OMagainOr, indeed, a bottle of whiskey….

BlasAnd still all the people that posts here beleive the fact that all the life beeing descent from a FUCA.

petrushkaDid I miss something that merits the “And still…”