Remix.run Logo
Truth is not a direction: a Tarski attack on LLM probes(abeljansma.nl)
81 points by abelaer 2 days ago | 33 comments
kstenerud 2 hours ago | parent | next [-]

> It might seem absurd to you to even suggest superhuman AIs could function as a truth-oracle (it certainly does to me), but there are two reasons to take it seriously. First, it is how these things will be used practically by the vast majority of people. They are already replacing standard Google search results, and I’ve had many discussions end with people delegating final authority on the truth to an AI.

There are already organizations taking advantage of this, actively producing "AI propaganda", meaning propaganda aimed at the LLMs themselves in order to influence their understanding of what is truthful and bend it towards powerful actors' agendas. They're not even hiding the fact that they're doing this.

Legend2440 5 hours ago | parent | prev | next [-]

I think this article pushes the premise farther than is reasonable.

The best anyone expects from an LLM "truth vector" is that it would encode the model's belief about whether the statement is true. Of course a perfect truth oracle is impossible.

samlinnfer an hour ago | parent | next [-]

Ah but is the model's belief of the statements 1. complete, 2. consistent, 3. decidable?

Terr_ 2 hours ago | parent | prev | next [-]

> The best anyone expects from an LLM "truth vector" is that it would encode the model's belief about whether the statement is true.

I think even that's too-optimistic: The LLM is a document-extender, so its "belief" is whether a token seems like it would statistically fit-next in a partial document, based on prior documents. This is usually not the kind of analytic truth we're interested in, and we've already figured out how to constantly extract it.

If we peek at vectors and weights, we'll we'll probably end up measuring the moods and styles for whatever tokens are about to get emitted next, whether that's dialogue for a fictional character (of various kinds), a narrator, or an impersonal memo conclusion paragraph. We'll be measuring "earnestness and conviction", on the same level as "loquaciousness" or "pleading" or "talking like a pirate."

So is Truthiness [0] what we really want? Probably not. If our document described the character as Yoda, then The Force connecting all existence ends up truthy. Using "a really gullible person" can repeat anything you supply as truthy. Even if we set things up as "a respected encyclopedia article" or "a relentlessly logical super-genius", we're really changing the influence mix of styles and biases, rather than creating a logical mind independent of text inside the LLM.

[0] https://en.wikipedia.org/wiki/Truthiness

TZubiri 5 hours ago | parent | prev [-]

If anything, the whole vector space is the LLM's truth.

zarzavat 4 hours ago | parent [-]

LLMs are not optimized only for truth they are optimized for a more complicated objective that includes e.g. humans liking their output. It is a universal truth that to get humans to like you, you have to lie to them.

elendilm 2 hours ago | parent | next [-]

<It is a universal truth that to get humans to like you, you have to lie to them.>

You don't represent all of us buddy. Some of us love truth above all else.

ngruhn an hour ago | parent [-]

Not many though

NitpickLawyer 3 hours ago | parent | prev [-]

> It is a universal truth that to get humans to like you, you have to lie to them.

Thus said HAL9000

aesthesia 6 hours ago | parent | prev | next [-]

Fun, though as hinted at the end, the point of LLM "truth" probes is to measure the model's internal judgment of truthfulness. There's no reason this judgment, even if measured with 100% accuracy, couldn't be mistaken or logically inconsistent.

baq an hour ago | parent | prev | next [-]

Title is a bit clickbaitish, but the content is well worth reading - came in with my pitchfork ready and left agreeing with basically all of it, with questions like ‘what if the probe could return 3 dimensions: truthfulness, knowledge confidence and decidability?’

Also the observation that people treat LLMs like oracles when they’re everything but is spot on, something I’ve also been thinking about and it’s quite a bit scary.

ziofill 5 hours ago | parent | prev | next [-]

A direction that is 99.99% accurate survives this argument completely. For all practical purposes one does not need totality.

customguy an hour ago | parent | next [-]

For a one time coin flip, sure. For a lot of them, depending on the stakes, that can be very, very wrong.

https://www.google.com/search?q=why+99.99+accuracy+is+not+en...

It doesn't take a lot of thought experiments to realize this. Imagine if every bite of food we eat had a 0.01% chance to turn into something instantly lethal in our mouth. Average lifespans would be reduced measurably, and apart from anxiety, we'd develop all sorts of strategies and laws around that. E.g. absolutely NO eating for airplane pilots. You wouldn't go on a date to have dinner, dancing and sex, you'd go dancing and have sex, and then have breakfast. People would modify their jaws and stomachs so they could eat less, but bigger chunks of food. It would be a whole thing!

And that's not even talking about water changing on us, or a tiny chance of getting sucked into the toilet whenever we use it, and a lot of other things where going from damn near 100% to 99.99% would change everything for the worse, by so much.

voxl 2 hours ago | parent | prev [-]

A basic course in statistics will inform you of why a 99.99% accurate test should be looked at with skepticism when diagnosing a rare disease. Yet we see the fancy 9s and think somehow this many 9s is enough.

ziofill 2 hours ago | parent | next [-]

Sure, but that’s not what we are talking about

ulrikrasmussen 16 minutes ago | parent [-]

Diagnosis of rare diseases is a subset of "true" statements, no?

elendilm 2 hours ago | parent | prev [-]

Really? Laws of probability works against your argument.

Such a basic course in statistics needs to be scrutinized.

californical 8 minutes ago | parent [-]

Every breath you take, there is a 99.99% chance that everything is normal, and a 0.01% chance that you breathe mild acid which horribly burns and causes a massive coughing fit.

It probably don’t cause long term damage unless that breath happened to be more important than normal, like while driving right as a child runs into the road.

Would you act differently knowing that you had one of these occasional acid breaths? Even if it only happened once per day on average (0.001%)

gdiamos 2 hours ago | parent | prev | next [-]

I wish I could get a model to state its assumptions.

reichstein 39 minutes ago | parent [-]

Models do not have assumptions. They have probabilities for what the next token should be. With enough context, in the context window and built into the model, that next token isn't completely random, it's correlated with something someone might choose to write.

But people write all kinds of crap manually. So far, the data people have been writing has tended to be denser around what people could agree on (there are many lies, but only one truth), so the model is more likely to go there.

If we start putting AI generated text into the training data, it's not clear what that means for the resulting model. It's already clear that some actors are trying to influence models by putting large amounts of content out there that agree with them.

Figuring out which content is safe to train from is the real problem for future model trainers.

scotty79 an hour ago | parent | prev | next [-]

> this sentence has no proof

As a programmer I was never impressed in such paradoxes. For me it was kinda obvious that in any sufficiently complex language you can create eqivalent of buggy infinite loop/recursion.

Vecr 5 hours ago | parent | prev | next [-]

Someone at MIRI must know how to solve this. Good luck getting them to tell you how!

saithound 5 hours ago | parent | prev | next [-]

It looks like Zach Weinersmith predicted this exact line of research 11 years ago [1], when he suggested testing the liar sentence using fMRI.

The same analysis applies: the probe tells us what the LLM thinks about the truth value if the sentence, not the truth value of the sentence. I don't think anyone claimed that these probes were truth oracles.

[1] https://smbc-comics.com/index.php?id=3657

TZubiri 5 hours ago | parent | prev [-]

Aren't there definitions of Truth that are not the negation of Falsehood? Can't there be a function True(x) that is not equal to !False(x)? Can't there be a third function Paradox(x) such that these counterexamples can be considered paradoxes and therefore outside of the truth?

I'm admittedly not a logician and don't formally study paradoxes, but I never quite understood the whole category of "this sentence is false" paradoxes, I feel that the sentence is paradox and therefore it's neither false nor true.

I do agree that it's a truth vector sounds like a silly panacea fantasy, though. But more logical formality is not the counter argument that would convince me of it, rather I believe that there's less formal and rigorous ways to get closer to truth.

galaxyLogic 4 hours ago | parent | next [-]

Interesting point about "self-referential sentences". I tend to agree. In my view a sentence saying something like "This sentence ..." does not have valid semantic meaning. It says nothing because, what "This" in "This sentence" means is ill-defined.

If terms we use are not well-defined, then sentences using such terms can not have meaning.

But for the sake of argument let's explore, what could the "this" in (so called) "self-referential" sentences refer to?

Do they refer to a specific encoding of the sentence you are reading, as some bits in computer memory perhaps?

That would require that those bits somehow have a unique "identity" and the "this" in a self-referential sentence would have to refer to those bits in specific addresses of a specific memory-chip.

But of course the "this" does not specify which memory chip, which specific (concrete) encoding of its (purported) meaning it is referring to. And if it did, then it would be talking about that specific set of bits in that specific memory-chip, not of "itself".

The fallacy is that what we perceive as a "sentence we read" is somehow "speaking" of something. But no, the sentence is not a subject, a sentence can not speak, and THEREFORE it specifically can not speak of itself.

A sentence can not speak, only actors, only subjects, like humans and AI, can "speak". And their speech must be encoded in some physical medium. A written sentence like "This sentence is ..." gives us the false impressions that somehow the SENTENCE IS SPEAKING of itself!

But speech can not speak, speech is the product of speaking.

Hence, in my view, "self-referential sentences" do not have any meaning and whatever paradoxes they might seem to create are results of confusion between ontological levels of "Subject" vs. "Speech".

aesthesia 2 hours ago | parent | next [-]

Quines produce similar issues to self-referential sentences without being directly self-referential. e.g. "'Yields falsehood when preceded by its quotation' yields falsehood when preceded by its quotation."

TZubiri an hour ago | parent [-]

> "'Yields falsehood when preceded by its quotation' yields falsehood when preceded by its quotation."

Here be the limits of my brain.

It does feel (vibes) like an obfuscation of the self-referential canonical 'This sentence is false' example, like a sum of obfuscation techniques that are designed to confuse, but don't materially change the nature of the phenomenon:

1- reference is made implicit, instead of explicit

2- References another object, necessitating (at least) two instances of the same sentence, with one referencing the other.

3- Maybe some unnecessarily complex language that could be made simpler?

So what I'm getting out of it is that it feels like a mental trap that is hard to compute and understand because it was designed that way (or because it evolved that way), not necessarily because of it containing a fundamentally useful knowledge, it's difficulty to parse IS itself the interesting property of the sentence.

Maybe meta analysis like looking into the history of this sentence and seeing how many people went crazy going down that rabbit hole would be more enlightening than engaging in it in good faith. Which might only be useful if you have a high enough IQ that it doesn't confuse you any longer.

erehweb 2 hours ago | parent | prev [-]

As the article notes, the sentence "This sentence is written in English" is well understood, and true. "This sentence is written in French" is also well understood and false.

TZubiri 2 hours ago | parent [-]

Right, my original comment wasn't about self-reference, but paradoxes, and not all self-references result in paradoxes.

Not sure what the difference between the language of a sentence and the truthiness of a sentence is. Maybe it has to do with the fact that the language refers to syntactical features that can be determined at 'compile' time, while truthiness refers to a semantic quality feature that can only be determined at 'runtime'. (See en.wikipedia.org/wiki/colorless_green_ideas_sleep_furiously for at the very least a funny canonical example of a syntactically valid, but semantically nonsensical sentence.)

The fact that the language function can also be mapped to reduced parts of the sentence, might also be relevant, you can deduce that "This-" and "This sentence is-" are English, while you cannot partially compute that "This sentence is-" is true. A single negation bit being enough to change the result of the operation.

codechicago277 3 hours ago | parent | prev | next [-]

I’m not a logician either but believe this is what Tarski’s definition of truth solves for. In order to make a statement about the statement itself, you have to introduce a new meta language. Then a statement in the meta language is only true if the underlying statement is true.

Much more rigorous explanation: https://plato.stanford.edu/entries/tarski-truth/

roywiggins 4 hours ago | parent | prev | next [-]

There is no lack of more elaborate logics:

https://en.wikipedia.org/wiki/Non-classical_logic

UltraSane 4 hours ago | parent | prev | next [-]

There are a LOT of different logical system.

Paraconsistent Logic

Intuitionistic Logic

Dialetheism

cgio 4 hours ago | parent | prev [-]

Fuzzy logic?