An important part of clearer thinking is rationality. But what is rationality, exactly? While you’ve probably heard this term, its precise meaning is often vague.
In this comprehensive guide about rationality, we answer many common questions, such as:
What is rationality?
Why is rationality important?
Where does rationality come from (and how can you become more rational)?
Does rationality really exist?
What is bounded rationality?
What is the difference between rationality, reason and intelligence?
In this first part of the guide, we’ll tackle the first question: What is rationality? To find out when we launch the second part, subscribe to our newsletter.
What is rationality?
Rationality can be divided into two aspects: epistemic rationality and instrumental rationality.
Epistemic rationality is the capacity and propensity to form accurate beliefs that map onto reality. People with greater epistemic rationality tend to form more accurate conclusions based on the information and evidence they encounter, and seek out evidence in such a way as to accurately arrive at the truth on topics that are important to them.
Instrumental rationality, on the other hand, is the capacity and propensity to choose our actions so as to effectively pursue our goals and values. People with greater instrumental rationality tend to make decisions in such a way that they achieve what they are aiming to achieve.
Epistemic rationality and instrumental rationality are related. It’s hard to pursue your goals if you’re mistaken about reality, and misconceptions about reality on important topics will often cause people to take unhelpful actions that move them away from (rather than toward) their goals.
Understanding and using epistemic rationality
Epistemic rationality helps you know what’s true about the world — even when the truth is painful or confusing. An epistemically rational person is good at assessing evidence, responding to new information, and proactively seeking out the truth.
What does this mean exactly? Let’s consider an example: in July 2023, David Grusch, a former US intelligence officer, made the surprising claim that the federal government was hiding evidence that aliens had visited earth. A person who prizes (epistemic) rationality will respond to new information like this in certain ways. They might ask themself questions like the following:
How should I respond to new information?
Let’s say that before hearing this report, you didn’t believe that aliens had visited earth. Is this evidence strong enough to change your mind? Or, if you were inclined to believe that aliens have visited earth, but you were unsure, does this evidence make you more certain?
Many people find it useful to think about beliefs on important and complex topics using probabilities. Rather than saying either ‘I think aliens have visited earth’ or ‘I think aliens haven’t visited earth’, they assign a probability (a credence) to the claim: for example, ‘I think there’s a 5% probability that aliens have visited the earth’.
If you assign probabilities to your beliefs, when you hear new evidence — for example, that a government official claims to know about a secret program to reverse-engineer UFOs — you can use this evidence to update your credence in the claim – for example, from 5% to 10%. In that case, you’d still believe, on balance, that no extraterrestrials have visited earth – but you’d now think that alien visits are slightly less unlikely than you did before.For more on updating your beliefs in response to new evidence, check out our free interactive tool on The Question of Evidence.
How can I keep an open mind (but without being gullible)?
We tend to have a bias towards interpreting information in a way that conforms to what we already believe; this is known as confirmation bias. A person who already suspects that aliens have visited earth is primed to believe Grusch’s allegations, whereas someone who is extremely skeptical about aliens is likely to assume he’s lying or confused. It’s ok to have strong opinions, particularly if you’ve thought about a topic a lot, but the heart of epistemic rationality is being open to the possibility that you’re wrong and adjusting your beliefs as you encounter new evidence.
Where can I find reliable information?
Not all sources of information are equally useful. If you’re trying to understand the world, which should you pay more attention to: academic research? The news? Self-proclaimed experts on TV? Friends? Personal blogs? Advertisements? Your opinionated uncle?
People who are more epistemically rational think hard about where their information comes from, and put more weight on information from more reliable sources. In this case, they might primarily be concerned with whether Grusch and his sources are reliable authorities.
Epistemic rationality isn’t the same as a good education. Someone who goes to a good school and college may well end up with lots of correct beliefs about their topic area of study, even if they just believe everything they are taught. However, sometimes teachers may present false information, or students may struggle to autonomously incorporate new evidence and prevent self-deception and bias outside the classroom, unless they also cultivate epistemic rationality.
Understanding and using instrumental rationality
Epistemic rationality helps you create a better map of the world; instrumental rationality, on the other hand, helps you use that map to get where you want to go. Instrumental rationality is about strategically pursuing what you deeply value. How can you choose actions that will help you achieve your goals? And more broadly, how do you select goals that genuinely reflect your values?
Let’s imagine a young person who is trying to decide what to do after high school. Should they go to college — and if so, where? Should they get a job —and if so, what? Or should they take some time off — and if so, what should they do?
If they wanted to approach this in an instrumentally rational way, they might ask themselves questions like:
How will the choices available to me impact whether I achieve my goals?
If this young person wants to become a doctor, it probably makes sense for them to go to college, or to take time off to volunteer doing something related to medicine. If their goal is to become an entrepreneur or business owner, college might still be a good option, but they might instead seek work in a field they’re interested in. If they want to become an artist, they might want to go to art school, or just work at their own art for a while. On the other hand, if they’re very tired after high school exams, a little time off might help them regain their energy, which will help them achieve other goals down the line.
How can I get the things I value?
On a larger scale, they will want to think about what their goals should even be, based on what they care about. If one of their intrinsic values is freedom, and a certain amount of money is needed to achieve that freedom, they may want to pursue a job or degree program that will eventually enable them to earn enough. If they deeply value tranquility, they might choose a less demanding school or a job that lets them spend a lot of time in nature.
Sometimes people confuse the idea of being instrumentally rational with being self-interested. Economics researchers develop models based on hypothetical agents who are both rational and self-interested, causing these two ideas to be conflated. But, in fact, you can be rational and highly altruistic. In that case, you’ll use your instrumental rationality to help you achieve your altruistic goals, as well as your selfish ones. For example, rationality can help an animal rights advocate to evaluate which strategies help animals the most; or a parent who wants to help their severely sick child can use rationality to decide what to do when doctors give conflicting advice.
Cognitive biases and rationality
An important aspect of rationality is the avoidance (or reduction) of cognitive biases. A cognitive bias is an irrational pattern in human judgment, thinking, decision-making or behavior.
Experimental psychology has discovered various ways in which our thinking is systematically skewed and distorted. These cognitive biases are very common in human behavior. You can probably observe many of them in your own life. Biases can interfere with both epistemic rationality (preventing you from believing what's true) and instrumental rationality (causing your decisions to be less effective at getting you what you value). While it is impossible to fully eliminate cognitive biases, we can reduce them to increase our rationality.
Social science has undergone a "replication crisis", and there are some cognitive biases that have had replication challenges. There are also substantial debates around how to interpret some experimental findings on cognitive bias, and how irrational or rational human behavior really is. However, the cognitive bias literature has mostly stood the test of time.
Some examples of cognitive biases are:
Confirmation bias: we’re more willing to take on board information that confirms what we already believe, while ignoring or dismissing contradictory evidence. We tend to interpret evidence in such a way that it seems to support our pre-existing beliefs
Availability bias: we tend to believe things happen more often when we can more easily think of examples of them happening, even though our ability to recall examples doesn't necessarily reflect the true frequency of events
Planning fallacy: we tend to underestimate how long large projects will take to finish and how much they will cost
Anchoring bias: we are sometimes influenced by irrelevant numbers; for instance, when we negotiate prices, the price we accept may be influenced by an initial figure made up by the person we’re negotiating, even though that number may have come from thin air
The fundamental attribution error: we tend to attribute our successes to our traits and character, but our failures to external factors (such as other people's behavior, or bad luck); but when assessing others, we are more likely to do the opposite. (However, some psychologists have found it a challenge to replicate the fundamental attribution error in experiments).
The endowment effect: we tend to overvalue things we own (relative to equivalent items that we don't own).
Typical minding: we tend to assume that others are like us and share our opinions, psychology, and behaviors when in reality, people vary widely
IKEA effect: we overvalue things we have made ourselves (for example, we may be especially attached to IKEA furniture that we assembled ourselves!)
For more, see our List of common cognitive biases.
Because these cognitive biases are ubiquitous, rationality is sometimes defined in terms of avoiding these biases, and many rationality techniques aim to combat these common human tendencies.
Why does rationality matter?
Epistemic rationality is about systematically improving our ability to form accurate beliefs, while instrumental rationality is about strategically achieving goals. If you aspire to have a tangible effect on the world — whether for your own benefit, or that of your loved ones, community, or society at large — you’ll need effective strategies. Without a sufficient degree of epistemic rationality, your actions may not respond to the world as it actually is; without enough instrumental rationality, your actions might not actually help you achieve what you want.
Rationality alone won’t make you successful — if your goals are hard to achieve, things like determination, grit, intelligence, skill, wealth, social skills, social networks, and creativity might also be important. However, rationality can help you make the best of these resources, and too little of it may be an impediment.
On the individual level, rationality can help you have the life you want. Let’s imagine someone who is trying to decide whether to move to a new city to take a new job, or stay where they are and keep their current job. How can they make a good decision? Well, they need to be able to form accurate beliefs about the world. They also need to avoid status quo bias – the tendency to stick to the default option. This might involve asking complex questions such as: what can they expect in their current job? What will their new job be like? What will it be like in the new city? They may want to reflect about how the change would fit into their life: would it help them better achieve their own values, whether that’s a more engaging work life, money, social impact, or a combination? Rationality is a set of skills that can help you navigate thorny questions like these.
In our daily lives, rationality can help us make better decisions. Consider a situation where you are seriously ill with a condition for which no standard medications exist, such as "chronic fatigue syndrome". Should you turn to alternative treatments like crystal healing, explore off-label experimental drugs, or try an intense exercise regimen? Many patients need to draw on their own rationality skills when, for example, different doctors offer them conflicting opinions, or when they encounter alternative sources of medical information, and they have to navigate a complex landscape of contradictory information and evidence.
On a broader, societal scale, rationality is perhaps even more important. You only have to read the news to know that our world is beset with incredibly serious and complex problems. Millions live in poverty, or suffer abuse and exploitation. Many die of preventable diseases, and other diseases don’t have a cure. Wars and violence are widespread. We only stand a chance of addressing these problems if we can think clearly about their causes and solutions.
This is particularly clear when problems come from a lack of knowledge. For example, when the COVID-19 pandemic first arose, there was no standard precedent we could follow about how to act, and there were many uncertainties about the disease. Many people felt they had no choice but to reason for themselves about what actions made the most sense. Scientists had to work out how to develop an effective vaccine. Politicians had to decide which social policies to implement: for example, how to balance the possible health benefits of stay-at-home mandates against damage to the economy and disruption to people’s lives. And individuals had to decide whether and when they should isolate, wear masks, and get vaccinated. In situations such as this, an ability to approach problems rationally is a great advantage.
You might think that our biggest societal problems spring not from a lack of knowledge, but from people acting in selfish or destructive ways without concern for others, particularly powerful people such as politicians or the wealthy. However, even from this perspective, rationality can help us devise effective strategies to oppose these bad actors. For example, if you are worried that a certain ideology is causing harm, rationality can help you think through the complexities of how best to oppose it — for example, should you lobby politicians, lead a protest, engage in civil disobedience, or write articles denouncing the group?
Rationality is also very important in the realm of research: both scientific and journalistic. Scientists try to answer complex and highly ambiguous questions. To do this, they need to assess evidence, formulate hypotheses, design experiments to test those hypotheses, and interpret the results without bias — even if those results disprove their favorite hypotheses that they have spent years developing. To do this well requires working to avoid cognitive bias and to think rigorously. As famed physicist Richard Feynman once put it:
“Science is a way of trying not to fool yourself. The principle is that you must not fool yourself, and you are the easiest person to fool.”
Rationality is also important in journalism. Journalists often address questions that are fuzzy and subjective yet vitally important, such as “is nuclear power beneficial for society?”, or questions that are harder to test, such as “did such-and-such really commit the crime they’ve been accused of?” Rational thinking can help journalists present a balanced perspective: this might involve evaluating how reliable their sources are, recognising contradictions, and synthesizing evidence from various perspectives.
What makes people rational?
Where does rationality come from? Is it innate or learnt?
It’s a bit of both. Some personality and psychological traits probably help people be more rational, and most psychological traits come about through a mix of nature and nurture. For example, some people may be born with greater aptitude at logical reasoning, but we can also improve our logical reasoning through learning and practice. Though logical reasoning is far from the whole of rationality, it’s one element of it.
Another important part of rationality is being in touch with your emotions and intuitions, since our emotions and intuitions often contain useful information. If you can sense and name your own feelings, you can have a clearer sense of what you actually want and where your uncertainties lie. Additionally, when we have consistent feedback, our intuitions develop over time: for example, a chess player will hone their intuitions about good gameplay by playing many games. Being able to tap into those useful intuitions can improve our decision-making.
People also vary in terms of how much their emotions align with reality. Our emotions can tell us things about the world and motivate us to take useful actions: for example, sadness can tell us that we’ve lost something valuable, or fear can warn us that a situation is dangerous. It’s a common misconception that rational people are not emotional: if you’re really in a dangerous situation, it’s rational and useful to be very afraid! But in practice, sometimes our emotions can bias us, and get in the way of assessing situations objectively. Proportionate anger can be a helpful sign that our boundaries have been crossed; but you probably know someone who gets angry at the slightest provocation, and someone else who never gets angry, even when they’re treated appallingly. Strong emotional tendencies like this can pull against rationality.
Media representations of emotionless, flat, "rational" characters like Spock from Star Trek can make emotionlessness seem rational, whereas actual rationality involves using your emotions as useful sources of information without letting them take control in situations where they aren't useful or are counterproductive.
Whatever your personality, the good news is you can train yourself to be more rational.
For example:
You can improve your ability to update your beliefs in response to new information.
You can learn how to make better plans by more reliably estimating how long things will take.
You can learn to become more in touch with your emotions (e.g., some people find techniques like Focusing helpful for this)
You can learn about cognitive biases, and practice identifying and avoiding them
You can practice calibrating your judgment and perceiving how sure you are about something, so you make fewer mistakes through over- or underconfidence.
You can learn common rhetorical fallacies, so you are less likely to be swayed by bad but persuasive arguments.
You can achieve your goals better by challenging self-limiting beliefs and learning healthier coping strategies.
See the section ‘Bounded rationality’ for more ways you can incorporate rationality into your life, and our website for more learning tools.
Does rationality really exist?
Rationality may sound like a rather vague idea. As certain online comment sections will show you, people often strongly disagree about what’s rational and what’s completely irrational! Most people think they are the rational ones, and those who say things they strongly disagree with are being irrational. And of course, definitions of abstract concepts such as rationality are often tricky to get right. We perhaps shouldn’t expect that rationality as a concept will be perfectly well-defined.
Nonetheless, it does make sense to think about being more rational, learning rationality techniques, and avoiding irrationality. Let’s consider how we defined rationality earlier: epistemic rationality is about improving our capacity to form accurate beliefs that map onto reality, and instrumental rationality helps us to strategically and effectively pursue our goals and values. Are some people better or worse at these things? Is it possible to be more or less in touch with reality, or more or less effective at achieving your goals? It seems clear that this is possible.
Consider two entrepreneurs who both have the goal of running a successful, profitable business, but who are working in a field they know little about. The first one gathers evidence about what customers want, then carefully thinks through that evidence, letting it inform their decisions. The second entrepreneur just makes their best guess about what customers will want, despite having no knowledge of the industry, and doesn't seek out evidence from the customers themselves. The first entrepreneur is applying some of the fundamental skills of rationality: seeking out evidence and carefully interpreting that evidence. The second entrepreneur is not. Which would you think is more likely to succeed, all else equal?
Bounded rationality: rationality within limits
There is one sense in which rationality doesn’t ‘really’ exist: it’s impossible for any human to be perfectly rational. Most (perhaps all!) of our actions are irrational to some extent, in the sense that they are not what we would do if we were perfectly rational; the aim of learning rationality techniques should be to reduce irrationality, not eliminate it.
Why isn’t anyone perfectly rational? Well, to start with, studies and everyday experience show that people often behave highly irrationally. But even beyond that, to be perfectly rational, a person would need to be a perfect thinker, and have unlimited time for thinking. Instrumental rationality is about choosing actions that are likely to help you achieve your goals. But the possible actions you could take at any given time are vast, and the possible ramifications of each action are broad and complex. The perfectly rational being would need to have unlimited thinking capacity: they’d need to be able to think as much they wanted instantly, and never make mistakes. They would then, when making a decision, consider all possible actions and all the possible ramifications of every action, and assess how probable each outcome was, and decide how each of those outcomes would advance their values if they happened; then, they’d choose the single action that was most likely to produce the most value (on average).
This is clearly beyond the capacity of even the smartest human. Let’s imagine you’re in a store, contemplating whether to buy a can of beans. If you were perfectly rational, and had unlimited thinking capacity, you would consider all the possible consequences of buying the beans and not buying them, and how likely and beneficial each was. You’d exhaustively survey all other possible things that you could buy instead and whether they would generate more value for you than the beans, and all the other ways you could spend your time if you walked out of the store and abandoned the beans. To be perfectly thorough, you may need to consider outlandish possibilities too, like ‘strip naked, throw the beans at the cashier, and run screaming from the store' — even though that’s very unlikely to be the best action, it has a tiny chance of being best.
Of course, with our limited thinking capacity, it makes sense not to worry about options like that, but with unlimited thinking capacity there would be no cost to considering even outlandish possibilities, just in case they turned out to be a good idea.
But for limited, real humans, instead of considering every possibility, it might be more rational to ask themself just one question depending on their goals. For example, if their goal is to eat healthily, they might ask ‘are beans healthy?’ If their goal is pleasure, they might ask ‘are beans tasty?’ Or if their goal is to save money, they might ask ‘does this can of beans fit within my budget?’
However, since we’re so limited, it might actually be irrational for a person to spend much time thinking about the beans at all; maybe they should just buy them if it feels right, and spend their brain cells considering more important questions.
‘Bounded rationality’ refers to the practice of trying to be as rational as possible given our constraints in time and brain power. Chidi from the sitcom The Good Place is a good example of a character who neglects bounded rationality: though he tries to make rational, ethical decisions, he spends too much time worrying about trivial things like whether he should use almond milk in his coffee, and ends up in a constant agony of indecision.
In the case of computers (real computers, not unboundedly powerful ones), we often use algorithms that apply heuristics. These involve considering only the most promising options, and ruling out others. A chess computer, for example, isn’t powerful enough to simulate every possible game continuation. But they can simulate a few steps ahead and choose the move that’s most promising based on patterns. This makes chess computers powerful enough to beat the top human chess players.
But what about humans? How can you practice good bounded rationality? Since we have severe limits to our time, and are far from perfect thinkers, we should take that into account when trying to behave rationally.
Some techniques we can use are:
Bounded Rationality Technique #1: Prioritization
Avoid spending too much time thinking about inconsequential decisions, or questions that don’t really matter. You probably don’t want to spend an hour deciding what movie to watch or whether to get Chinese or Mexican food tonight. If you’re making a decision — let’s say, what hobby to take up — it’s good practice to start by brainstorming and generating a lot of options. But you should quickly winnow these options back down: if you think you’re unlikely to really enjoy laughter yoga or roller derby, don’t spend hours googling clubs for those things in your area.
Bounded Rationality Technique #2: Opportunity cost
Things you do can cost money, but they can also cost time and opportunities. If you spend three hours at a concert, you can’t spend the same time seeing a movie, working, sleeping, visiting friends, or doing anything else you might want to do. So when considering whether to do something, consider not just whether it will be fun and useful, but also what alternatives you’re missing out on. However, we can't consider all of the opportunities you miss out on by doing another one, so it's worth focussing on just one or two of the most relevant opportunities.
Bounded Rationality Technique #3: Time-boxing
It’s good to think carefully about important decisions, but it can also be paralyzing. Additionally, for any given decision, there is a limit to how much time it is worth spending on it. A way to get around both of these issues is to time-box the thinking and research. For example, if a decision is somewhat important, but not that important, you could say ‘I'll give myself an hour to research and consider, and at the end of that, I’ll go with my best guess’.
Bounded Rationality Technique #4: Principles, policies and heuristics
One way to save time is to use decision systems and heuristics to make decisions. You can form principles or policies which tell you how to act in certain situations. For example, if you’re worried about the ethical impact of your diet, you might follow a principle such as sticking to a vegetarian diet, eating local, or abstaining from beef or palm oil (depending on your particular ethics and views): this takes less time than assessing the ethical impact of each meal on its own merits.
Bounded Rationality Technique #5: Habits
We all have many habits, good and bad. You might have a habit of morning coffee, an evening walk, or checking your email before bed. Since performing a habitual behavior is usually automatic —you don’t think hard about whether to do it each time — developing good habits and avoiding bad ones can be a good way of pursuing your goals while freeing up time and energy for other things. For example, if you like meditation and want to do it regularly, rather than deciding ‘should I meditate now, or do something else?’, you could try to build the habit of meditating at a certain time every day. Trigger-action planning is a method some find helpful for building habits. It involves practicing or rehearsing performing actions in response to a trigger (e.g. ‘every time I put my toothbrush back in its holder, I will pick up the jar of vitamins’).
Rationality, reason, intelligence and education
Rationality has some overlaps with reason, intelligence, and education, but it is distinct.
Rationality vs reason
When we talk about ‘using reason’ to make decisions, is that the same as rationality?
Just like ‘rationality’, the term ‘reason’ is used in many ways. However, when people talk about reason, they usually mean deduction or explicit thinking. For example, if you are working on a logic puzzle or trying to assess the rigor of a philosophical argument, you are probably relying heavily on reasoning.
Psychologist Daniel Kahneman popularized the idea of two thinking ‘systems’: one thinks quickly and instinctively (‘System 1’), the other considers things slowly and more explicitly (‘System 2’). When we answer a simple math problem (like 2+2=4), or react to catch a ball tossed to us, we're using the fast System 1, whereas when we’re trying to work out a much harder math problem (like 27 * 22) or figure out how a clock works, we're using our System 2. When we talk about ‘reason’, we usually mean System 2-driven, considered thinking. But rationality crucially involves being in touch with our System 1 as well as System 2, and training them to work together to our advantage.
To see why, consider that one of the benefits of rationality is that you’re better able to achieve your goals and values. You can’t do this if you’re not even sure what your values are, but understanding one's values involves both System 1 feelings and System 2 processing of those feelings. Often we feel internally divided: our ‘head’ might want one thing, our ‘heart’ another. Rationality involves not ignoring the heart, but incorporating both head and heart, both feelings and reason, into our decisions.
Another important aspect of rationality is being well-calibrated: knowing how certain you are, and having those feelings of certainty accurately reflect how often you actually are correct. If you can feel a gut sense of uncertainty that's in alignment with how likely things really are, you are less likely to act in an overconfident or underconfident way.
Rationality vs intelligence
Is rationality just about being smart? Rationality and intelligence are certainly related; intelligence makes it easier to learn rationality techniques and apply them creatively, all else equal. Intelligence can also help with logical thinking and reasoning, which are parts of rationality. Research by Keith Stanovich has found rationality and intelligence (as measured by IQ scores) to be substantially (but far from perfectly) correlated.
But it’s also possible to be smart and highly irrational. You might be good at solving mathematical puzzles or learning languages, but terrible at making good decisions, or very prone to cognitive biases. Some people have intelligence, but don’t apply it effectively to make their lives go better.
Intelligent people are more likely to believe and do things that are out of the ordinary, and are unusually good at justifying and arguing for their behavior – to themselves and others. This cuts both ways: it means that geniuses can be trailblazers and end up much more rational than their peers, but they can also go off the rails by being overconfident in outlandish ideas.
An intelligent person who really wants to figure out the truth might do better than a less intelligent person, but an intelligent person who wants to concoct an elaborate justification for a conspiracy theory will also be good at that. If your beliefs are really irrational, intelligence may only make them more entrenched.
Rationality vs education
If rationality is about forming true beliefs, isn’t that just good education? Good education is helpful for rationality; obviously, it’s more helpful to start out with a set of true beliefs than a set of lies. And the more accurate knowledge you have (for instance, from a good education), the easier time you will have understanding the world around you.
But good education can’t substitute for rationality. First, since rationality is about achieving one’s own values, no educational program is going to tell you exactly what to do: you have to work out how to apply general facts and principles you’ve been taught to your own life. Second, no education can teach you everything about the world. New events are constantly happening, and though a good education can give you a solid background and context, it can’t help you make sense of changes, or form good beliefs about what’s true today.
But most importantly, rationality skills are often not taught, or only taught to a limited degree, within formal education. For instance, students may be asked to solve math problems, but they are unlikely to be asked to (for instance) evaluate the evidence for and against a proposition, or to practice working with their emotions so that their emotions provide valuable insights without overwhelming them. Much of what it means to be rational is about developing, possessing and applying skills, and many of these skills are absent from standard education curricula.
We hope this post helps you understand what rationality is and why it matters! If you’re intrigued to learn more, we invite you to test your overall level of rationality, and what you can do now to improve your rationality skills, by completing our quiz "How Rational Are You, Really?".