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The Illusion of Thinking: Understanding the Limitations of Reasoning LLMs [pdf]

throwaway71271

I think one of the reason we are confused about what LLMs can do is because they use language. And we look at the "reasoning traces" and the tokens there look human, but what is actually happening is very alien to us, as shown by "Biology of Large Language Models"[1] and "Safety Alignment Should Be Made More Than Just a Few Tokens Deep"[2]

I am struggling a lot to see what the tech can and can not do, particularly designing systems with them, and how to build systems where the whole is bigger than the sum of its parts. And I think this is because I am constantly confused by their capabilities, despite understanding their machinery and how they work, their use of language just seems like magic. I even wrote https://punkx.org/jackdoe/language.html just to remind myself how to think about it.

I think this kind of research is amazing and we have to spend tremendous more effort into understanding how to use the tokens and how to build with them.

[1]: https://transformer-circuits.pub/2025/attribution-graphs/bio... [2]: https://arxiv.org/pdf/2406.05946

curious_cat_163

> Rather than standard benchmarks (e.g., math problems), we adopt controllable puzzle environments that let us vary complexity systematically

Very clever, I must say. Kudos to folks who made this particular choice.

> we identify three performance regimes: (1) low complexity tasks where standard models surprisingly outperform LRMs, (2) medium-complexity tasks where additional thinking in LRMs demonstrates advantage, and (3) high-complexity tasks where both models experience complete collapse.

This is fascinating! We need more "mapping" of regimes like this!

What I would love to see (not sure if someone on here has seen anything to this effect) is how these complexity regimes might map to economic value of the task.

For that, the eval needs to go beyond puzzles but the complexity of the tasks still need to be controllable.

null

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antics

I think the intuition the authors are trying to capture is that they believe the models are omniscient, but also dim-witted. And the question they are collectively trying to ask is whether this will continue forever.

I've never seen this question quantified in a really compelling way, and while interesting, I'm not sure this PDF succeeds, at least not well-enough to silence dissent. I think AI maximalists will continue to think that the models are in fact getting less dim-witted, while the AI skeptics will continue to think these apparent gains are in fact entirely a biproduct of "increasing" "omniscience." The razor will have to be a lot sharper before people start moving between these groups.

But, anyway, it's still an important question to ask, because omniscient-yet-dim-witted models terminate at "superhumanly assistive" rather than "Artificial Superintelligence", which in turn economically means "another bite at the SaaS apple" instead of "phase shift in the economy." So I hope the authors will eventually succeed.

imiric

> I think the intuition the authors are trying to capture is that they believe the models are omniscient, but also dim-witted.

We keep assigning adjectives to this technology that anthropomorphize the neat tricks we've invented. There's nothing "omniscient" or "dim-witted" about these tools. They have no wit. They do not think or reason.

All Large "Reasoning" Models do is generate data that they use as context to generate the final answer. I.e. they do real-time tuning based on synthetic data.

This is a neat trick, but it doesn't solve the underlying problems that plague these models like hallucination. If the "reasoning" process contains garbage, gets stuck in loops, etc., the final answer will also be garbage. I've seen sessions where the model approximates the correct answer in the first "reasoning" step, but then sabotages it with senseless "But wait!" follow-up steps. The final answer ends up being a mangled mess of all the garbage it generated in the "reasoning" phase.

The only reason we keep anthropomorphizing these tools is because it makes us feel good. It's wishful thinking that markets well, gets investors buzzing, and grows the hype further. In reality, we're as close to artificial intelligence as we were a decade ago. What we do have are very good pattern matchers and probabilistic data generators that can leverage the enormous amount of compute we can throw at the problem. Which isn't to say that this can't be very useful, but ascribing human qualities to it only muddies the discussion.

antics

I am not sure we are on the same page that the point of my response is that this paper is not enough to prevent exactly the argument you just made.

In any event, if you want to take umbrage with this paper, I think we will need to back up a bit. The authors use a mostly-standardized definition of "reasoning", which is widely-accepted enough to support not just one, but several of their papers, in some of the best CS conferences in the world. I actually think you are right that it is reasonable to question this definition (and some people do), but I think it's going to be really hard for you to start that discussion here without (1) saying what your definition specifically is, and (2) justifying why its better than theirs. Or at the very least, borrowing one from a well-known critique like, e.g., Gebru's, Bender's, etc.

tim333

>There's nothing "omniscient" or "dim-witted" about these tools

I disagree in that that seems quite a good way of describing them. All language is a bit inexact.

Also I don't buy we are no closer to AI than ten years ago - there seem lots going on. Just because LLMs are limited doesn't mean we can't find or add other algorithms - I mean look at alphaevolve for example https://www.technologyreview.com/2025/05/14/1116438/google-d...

>found a faster way to solve matrix multiplications—a fundamental problem in computer science—beating a record that had stood for more than 50 years

I figure it's hard to argue that that is not at least somewhat intelligent?

imiric

> I figure it's hard to argue that that is not at least somewhat intelligent?

The fact that this technology can be very useful doesn't imply that it's intelligent. My argument is about the language used to describe it, not about its abilities.

The breakthroughs we've had is because there is a lot of utility from finding patterns in data which humans aren't very good at. Many of our problems can be boiled down to this task. So when we have vast amounts of data and compute at our disposal, we can be easily impressed by results that seem impossible for humans.

But this is not intelligence. The machine has no semantic understanding of what the data represents. The algorithm is optimized for generating specific permutations of tokens that match something it previously saw and was rewarded for. Again, very useful, but there's no thinking or reasoning there. The model doesn't have an understanding of why the wolf can't be close to the goat, or how a cabbage tastes. It's trained on enough data and algorithmic tricks that its responses can fool us into thinking it does, but this is just an illusion of intelligence. This is why we need to constantly feed it more tricks so that it doesn't fumble with basic questions like how many "R"s are in "strawberry", or that it doesn't generate racially diverse but historically inaccurate images.

Kon5ole

>They have no wit. They do not think or reason.

Computers can't think and submarines can't swim.

Jensson

But if you need a submarine that can swim as agiley as a fish then we still aren't there yet, fish are far superior to submarines in many ways. So submarines might be faster than fish, but there are so many maneuvers that fish can do that the submarine can't. Its the same with here with thinking.

So just like computers are better at humans at multiplying numbers, there are still many things we need human intelligence for even in todays era of LLM.

drodgers

> I think AI maximalists will continue to think that the models are in fact getting less dim-witted

I'm bullish (and scared) about AI progress precisely because I think they've only gotten a little less dim-witted in the last few years, but their practical capabilities have improved a lot thanks to better knowledge, taste, context, tooling etc.

What scares me is that I think there's a reasoning/agency capabilities overhang. ie. we're only one or two breakthroughs away from something which is both kinda omniscient (where we are today), and able to out-think you very quickly (if only through dint of applying parallelism to actually competent outcome-modelling and strategic decision making).

That combination is terrifying. I don't think enough people have really imagined what it would mean for an AI to be able to out-strategise humans in the same way that they can now — say — out-poetry humans (by being both decent in terms of quality and super fast). It's like when you're speaking to someone way smarter than you and you realise that they're 6 steps ahead, and actively shaping your thought process to guide you where they want you to end up. At scale. For everything.

This exact thing (better reasoning + agency) is also the top priority for all of the frontier researchers right now (because it's super useful), so I think a breakthrough might not be far away.

Another way to phrase it: I think today's LLMs are about as good at snap judgements in most areas as the best humans (probably much better at everything that rhymes with inferring vibes from text), but they kinda suck at:

1. Reasoning/strategising step-by-step for very long periods

2. Snap judgements about reasoning or taking strategic actions (in the way that expert strategic humans don't actually need to think through their actions step-by-step very often - they've built intuition which gets them straight to the best answer 90% of the time)

Getting good at the long range thinking might require more substantial architectural changes (eg. some sort of separate 'system 2' reasoning architecture to complement the already pretty great 'system 1' transformer models we have). OTOH, it might just require better training data and algorithms so that the models develop good enough strategic taste and agentic intuitions to get to a near-optimal solution quickly before they fall off a long-range reasoning performance cliff.

Of course, maybe the problem is really hard and there's no easy breakthrough (or it requires 100,000x more computing power than we have access to right now). There's no certainty to be found, but a scary breakthrough definitely seems possible to me.

sitkack

I think you are right, and that the next step function can be achieved using the models we have, either by scaling the inference, or changing the way inference is done.

danielmarkbruce

People are doing all manner of very sophisticated inferency stuff now - it just tends to be extremely expensive for now and... people are keeping it secret.

sitkack

There is no reason that omniscient-yet-dim-witted has to plateau at human intelligence.

antics

I am not sure if you mean this to refute something in what I've written but to be clear I am not arguing for or against what the authors think. I'm trying to state why I think there is a disconnect between them and more optimistic groups that work on AI.

drodgers

I think that commenter was disagreeing with this line:

> because omniscient-yet-dim-witted models terminate at "superhumanly assistive"

It might be that with dim wits + enough brute force (knowledge, parallelism, trial-and-error, specialisation, speed) models could still substitute for humans and transform the economy in short order.

teleforce

> We found that LRMs have limitations in exact computation: they fail to use explicit algorithms and reason inconsistently across puzzles.

It seems that AI LLMs/LRMs need helps from their distant cousins namely logic, optimization and constraint programming that can be attributed as intelligent automation or IA [1],[2],[3],[4].

[1] Logic, Optimization, and Constraint Programming: A Fruitful Collaboration - John Hooker - CMU (2023) [video]:

https://www.youtube.com/live/TknN8fCQvRk

[2] "We Really Don't Know How to Compute!" - Gerald Sussman - MIT (2011) [video]:

https://youtube.com/watch?v=HB5TrK7A4pI

[3] Google OR-Tools:

https://developers.google.com/optimization

[4] MiniZinc:

https://www.minizinc.org/

cdrini

When I use a normal LLM, I generally try to think "would I be able to do this without thinking, if I had all the knowledge, but just had to start typing and go?".

With thinking LLMs, they can think, but they often can only think in one big batch before starting to "speak" their true answer. I think that needs to be rectified so they can switch between the two. In my previous framework, I would say "would I be able to solve this if had all the knowledge, but could only think then start typing?".

I think for larger problems, the answer to this is no. I would need paper/a whiteboard. That's what would let me think, write, output, iterate, draft, iterate. And I think that's where agentic AI seems to be heading.

actinium226

Man, remember when everyone was like 'AGI just around the corner!' Funny how well the Gartner hype cycle captures these sorts of things

latchup

To be fair, the technology sigmoid curve rises fastest just before its inflection point, so it is hard to predict at what point innovation slows down due to its very nature.

The first Boeing 747 was rolled out in 1968, only 65 years after the first successful heavier-than-air flight. If you told people back then that not much will fundamentally change in civil aviation over the next 57 years, no one would have believed you.

bayindirh

They're similar to self-driving vehicles. Both are around the corner, but neither can negotiate the turn.

nmca

I saw your comment and counted — in May I took a Waymo thirty times.

bayindirh

Waymo is a popular argument in self-driving cars, and they do well.

However, Waymo is Deep Blue of self-driving cars. Doing very well in a closed space. As a result of this geofencing, they have effectively exhausted their search space, hence they work well as a consequence of lack of surprises.

AI works well when search space is limited, but General AI in any category needs to handle a vastly larger search space, and they fall flat.

At the end of the day, AI is informed search. They get inputs, and generate a suitable output as deemed by their trainers.

hskalin

And commerically viable nuclear fusion

mgiampapa

I harvest fusion energy every single day... It's just there in the sky, for free!

kfarr

Waymo's pretty good at unprotected lefts

bayindirh

Waymo is pretty good at (a finite number of) unprotected lefts, and this doesn't count as "level 5 autonomous driving".

einrealist

All that to keep the investment pyramid schemes going.

brookst

…but that was, like, two years ago? If we go from GPT2 to AGI in ten years that will still feel insanely fast.

tonyhart7

I think we just around at 80% of progress

the easy part is done but the hard part is so hard it takes years to progress

georgemcbay

> the easy part is done but the hard part is so hard it takes years to progress

There is also no guarantee of continued progress to a breakthrough.

We have been through several "AI Winters" before where promising new technology was discovered and people in the field were convinced that the breakthrough was just around the corner and it never came.

LLMs aren't quite the same situation as they do have some undeniable utility to a wide variety of people even without AGI springing out of them, but the blind optimism that surely progress will continue at a rapid pace until the assumed breakthrough is realized feels pretty familiar to the hype cycle preceding past AI "Winters".

Swizec

> We have been through several "AI Winters" before

Yeah, remember when we spent 15 years (~2000 to ~2015) calling it “machine learning” because AI was a bad word?

We use so much AI in production every day but nobody notices because as soon as a technology becomes useful, we stop calling it AI. Then it’s suddenly “just face recognition” or “just product recommendations” or “just [plane] autopilot” or “just adaptive cruise control” etc

You know a technology isn’t practical yet because it’s still being called AI.

mirekrusin

I remember "stochastic parrot" and people saying it's fancy markov chain/dead end. You don't hear them much after roughly agentic coding appeared.

yahoozoo

We will be treating LLMs “like a junior developer” forever.

JKCalhoun

And I'm fine with that.

sneak

Even if they never get better than they are today (unlikely) they are still the biggest change in software development and the software development industry in my 28 year career.

roenxi

What do you think has changed? The situation is still about as promising for AGI in a few years - if not more so. Papers like this are the academics mapping out where the engineering efforts need to be directed to get there and it seems to be a relatively small number of challenges that are easier as the ones already overcome - we know machine learning can solve Towers of Hanoi, for example. It isn't fundamentally complicated like Baduk is. The next wall to overcome is more of a low fence.

Besides, AI already passes the Turing test (or at least, is most likely to fail because it is too articulate and reasonable). There is a pretty good argument we've already achieved AGI and now we're working on achieving human- and superhuman-level intelligence in AGI.

MoonGhost

> What do you think has changed? The situation is still about as promising for AGI in a few years - if not more so

It's better today. Hoping that LLMs can get us to AGI in one hop was naive. Depending on definition of AGI we might be already there. But for superhuman level in all possible tasks there are many steps to be done. The obvious way is to find a solution for each type of tasks. We have already for math calculations, it's using tools. Many other types can be solved the same way. After a while we'll gradually get to well rounded 'brain', or model(s) + support tools.

So, so far future looks bright, there is progress, problems, but not deadlocks.

PS: Turing test is a <beep> nobody seriously talks about today.

thomasahle

All the environments the test (Tower of Hanoi, Checkers Jumping, River Crossing, Block World) could easily be solved perfectly by any of the LLMs if the authors had allowed it to write code.

I don't really see how this is different from "LLMs can't multiply 20 digit numbers"--which btw, most humans can't either. I tried it once (using pen and paper) and consistently made errors somewhere.

Jensson

> I don't really see how this is different from "LLMs can't multiply 20 digit numbers"--which btw, most humans can't either. I tried it once (using pen and paper) and consistently made errors somewhere.

People made missiles and precise engineering like jet aircraft before we had computers, humans can do all of those things reliably just by spending more time thinking about it, inventing better strategies and using more paper.

Our brains weren't made to do such computations, but a general intelligence can solve the problem anyway by using what it has in a smart way.

thomasahle

Some specialized people could probably do 20x20, but I'd still expect them to make a mistake at 100x100. The level we needed for space crafts was much less than that, and we had many levels of checks to help catch errors afterwards.

I'd wager that 95% of humans wouldn't be able to do 10x10 multiplication without errors, even if we paid them $100 to get it right. There's a reason we had to invent lots of machines to help us.

It would be an interesting social studies paper to try and recreate some "LLMs can't think" papers with humans.

Jensson

> There's a reason we had to invent lots of machines to help us.

The reason was efficiency, not that we couldn't do it. If a machine can do it then we don't need expensive humans to do it, so human time can be used more effectively.

jdmoreira

No. a huge population of humans did while standing on the shoulders of giants.

Jensson

Humans aren't giants, they stood on the shoulder of other humans. So for AI to be equivalent they should stand on the shoulders of other AI models.

Xmd5a

>Large Language Model as a Policy Teacher for Training Reinforcement Learning Agents

>In this paper, we introduce a novel framework that addresses these challenges by training a smaller, specialized student RL agent using instructions from an LLM-based teacher agent. By incorporating the guidance from the teacher agent, the student agent can distill the prior knowledge of the LLM into its own model. Consequently, the student agent can be trained with significantly less data. Moreover, through further training with environment feedback, the student agent surpasses the capabilities of its teacher for completing the target task.

https://arxiv.org/abs/2311.13373

someothherguyy

> humans can't

The reasons humans can't and the reasons LLMs can't are completely different though. LLMs are often incapable of performing multiplication. Many humans just wouldn't care to do it.

JusticeJuice

Their finding of LLMs working best at simple tasks, LRMs working best at medium complexity tasks, and then neither succeeding at actually complex tasks is good to know.

cubefox

Not sure whether I sense sarcasm.

nialv7

I've seen this too often, papers that ask questions they don't even bother to properly define.

> Are these models capable of generalizable reasoning, or are they leveraging different forms of pattern matching?

Define reasoning, define generalizable, define pattern matching.

For additional credits after you have done so, show humans are capable of what you just defined as generalizable reasoning.

NitpickLawyer

> show humans are capable of what you just defined as generalizable reasoning.

I would also add "and plot those capabilities on a curve". My intuition is that the SotA models are already past the median human abilities in a lot of areas.

crvdgc

In the context of this paper, I think "generalizable reasoning" means that finding a method to solve the puzzle and thus being able to execute the method on puzzle instances of arbitrary complexity.

null

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danck

In figure 1 bottom-right they show how the correct answers are being found later as the complexity goes higher. In the description they even state that in false responses the LRM often focusses on a wrong answer early and then runs out of tokens before being able to self-correct. This seems obvious and indicates that it’s simply a matter of scaling (bigger token budget would lead better abilities for complexer tasks). Am I missing something?

d4rkn0d3z

I wrote my first MLP 25 years ago. After repeating some early experiments in machine learning from 20 ywars before that. One of the experiments I repeated was in text to speach. It was amazing to set up training runs and return after seveal hours to listen to my supercomputer babble like a toddler. I literally recall listening and being unable to distinguish the output from my NN from that of a real toddler, I happened to be teaching my neice to read around that same time. And when the NN had gained a large vocabulary such that it could fairly proficiently read aloud, I was convinced that I had found my PHD project and a path to AGI.

Further examination and discussion with more experienced researchers gave me pause. They said that one must have a solution, or a significant new approach toward solving the hard problems associated with a research project for it to be viable, otherwise time (and money) is wasted finding new ways to solve the easy problems.

This is a more general principle that can be applied to most areas of endeavour. When you set about research and development that involves a mix of easy, medium, and hard problems, you must solve the hard problems first otherwise you blow your budget finding new ways to solve the easy problems, which nobody cares about in science.

But "AI" has left the realm of science behind and entered the realm of capitalism where several years of meaningless intellectual gyration without ever solving a hard problem may be quite profitable.

esafak

I don't know that I would call it an "illusion of thinking", but LLMs do have limitations. Humans do too. No amount of human thinking has solved numerous open problems.

th0ma5

The errors that LLMs make and the errors that people make are not probably not comparable enough in a lot of the discussions about LLM limitations at this point?

esafak

We have different failure modes. And I'm sure researchers, faced with these results, will be motivated to overcome these limitations. This is all good, keep it coming. I just don't understand the some of the naysaying here.

Jensson

They naysayers just says that even when people are motivated to solve a problem the problem might still not get solved. And there are unsolved problems still with LLM, the AI hypemen say AGI is all but a given in a few years time, but if that relies on some undiscovered breakthrough that is very unlikely since such breakthroughs are very rare.