Belief, reasons, knowledge and certainty

This famous line comes from Frank Herbert's science-fiction novel Dune Messiah. In full, the quotation reads: "They're trained to believe, not to know. Belief can be manipulated. Only knowledge is dangerous."

Believing

Everything begins with belief. As children, we initially believe everything our parents tell us. This childhood belief forms the basis on which we then build.

But children also have experiences and always ask: Why? Our parents don't have an answer to everything, and so at some point we learn a painful lesson: not everything we believe is also true. That is part of growing up.

And so we set out to search for answers ourselves.

Example

Why can't I keep partying with you? Because you have to sleep now.

Why do I have to sleep already? Because otherwise you'll be tired tomorrow and fall asleep at school.

Why do I have to go to school? Because there you learn what you need for your life, in order to earn money.

Why do I have to earn money? So that you can party later!

Types of belief (a helpful classification)

In philosophy, a distinction is often made according to what it is about (descriptive, normative, metaphysical) and according to how the belief comes about (experience, authority, inference, intuition).

Everyday basic assumptions and intuitions

We 'always already' implicitly presuppose:

• My memories are by and large reliable (and not constantly distorted after the fact).
• Other people have a consciousness like mine (and are not 'philosophical zombies').
• My perception normally represents the external world reasonably correctly (illusions are exceptions, not the rule).
• If most people independently report the same thing, then it probably happened that way.
• When I open the front door, there isn't suddenly an abyss there.
• When I wake up in the morning, I am really awake and not just dreaming it.
• When you walk behind the tree, you disappear behind the tree, and then a tiger doesn't suddenly come out on the other side, but you do. (Children often have such creative notions)
• If I measure a meter here and walk to the other end of the field, the meter stick is still exactly as long.¹
• My time on the sofa and yours in the car pass equally fast. Or, all clocks run equally fast. (this is intuitively correct, but as special relativity shows, not the case)
• If something is "natural", it tends to be good/healthy — and if something is "artificial", it tends to be bad/dangerous. (intuitively plausible, but often a fallacy)

We can already see that, simply in order to live, we have to presuppose an incredible number of things without constantly questioning them. We believe.

Explicit empirical beliefs — What is the world like in everyday life?

We believe many facts explicitly. These statements are fundamentally observable/testable (at least indirectly).

I believe:

• "A jump from the balcony of the 10th floor is life-threatening."
  • This is an everyday situation; it happens that people fall off buildings.
  • When we fall to the ground from a great height, that is usually the end of the story.
  • The vast majority of scientists agree here, and there is no conflict of interest as with climate change. (there are hardly any falling-off-a-building-is-dangerous deniers)
  • There is rarely fake news here: it is immediately testable, the result is unambiguous, and you can only be wrong once.
  • This situation is sometimes called the "causal near-field".

• "I run faster than my sister."
  • This is easy to understand and testable (stopwatch, distance, repetitions).
  • It may be true today; but tomorrow it can already be false again.

• "Nora probably ate the last cookie."
  • Here we can mount a proper forensic investigation. We have circumstantial evidence (who was there, typical preferences, alternatives) → inference to the best explanation.
    • I only saw Nora in the house and suddenly the delicious cookie was gone.
    • Cookies don't disappear on their own.
    • Nora likes cookies.
    • So it must have been Nora.
  • But it may be that we will never know; even if Nora admits she ate the cookie, she could be mistaken.

• "This swing will still hold this year."
  • Here I am putting my children's health at stake. So I want to be certain.
  • My reasons: the swing is only two years old and looks stable. I shook it; nothing moves.
  • But the sentence is not simply true or false, because it says something about the future of a particular swing.

We see that even in everyday life there are many different ways of believing something in the sense of "I believe that ...". In each of these cases, one question seems important to us:

Methodical doubt

Is what I believe also true?

Can I be wrong, and what reasons do I have to believe what I believe? That is the connection between belief and knowledge.

"Believing-in" as trust

We also use 'believe' to express that something is important to us. This is more like trust, not just as a truth concept but as a relational one.

• "I believe in you." (confidence)
• "I trust my colleague." (social reliability)
• "I believe in the communist party, it is always right." 😄
• "I believe in his honesty and sincerity."

Whether someone is really trustworthy cannot be determined, since it depends on the future (counterfactual). It is not a testable factual claim about the world, but rather an extrapolation from the past to the future.

Derived everyday beliefs from science — popularized knowledge

Many people adopt well-confirmed scientific findings as beliefs without knowing the studies themselves. They simply believe it. 😱

I believe:

• "Smoking increases the risk of cancer."
  • Smoking was for a long time simply really cool. Edward Bernays² staged cigarettes as a sign of women's emancipation.
  • Despite overwhelming evidence, the cigarette industry spread fairy tales and pseudoscientific studies for decades to play down the danger.
  • Who profits from the lie: the cigarette industry.

• "The Earth is (approximately) spherical."
  • This is totally counterintuitive, of course. We don't see the sphere, after all.
  • The hypothesis of the round Earth has existed since antiquity, but at the latest in the age of space travel it is generally accepted: now even the last doubter can see it.
  • Nevertheless, there are still people who even risk their lives to prove that the Earth is flat. Mad Mike 🚀
  • Who profits: those who wage the "war against the intellectuals"³.

• "The human-made share of climate change is considerable."
  • Have you read the latest IPCC report? No? Well, maybe the summary.
  • Most of us trust the scientific community⁴.
  • Most climate deniers have read nothing at all, have no clue about physics, confuse climate with weather. They simply don't want to.
  • Who profits: the fossil-fuel industry.

• "Near certain industrial facilities or power plants, increased health risks can occur."
  • The interesting question is then: how much risk am I willing to take in order not to jeopardize my prosperity.
  • Some prefer nuclear power plants despite their safety concerns, others prefer wind turbines: safer but ugly and annoying.

Normative (ought) beliefs — "What should one do?" (ethics/politics)

Here it is not (only) about facts, but about values and rules of action.

I believe:

• "One should help others when the costs are low."
• "The state should do more or less for pensions."
• "Punishments should rather deter or rather rehabilitate."
• "Violence against civilians is morally wrong."
• "A real family consists of father, mother and children / or other constellations are equally valid."
• "All human beings are born free and equal in dignity and rights. They are endowed with reason and conscience and should encounter one another in a spirit of solidarity."
  • Article 1 of the Universal Declaration of Human Rights⁵
  • This is an ethical principle, not a universal truth.

Many of our values are traditionally anchored and have proven themselves, others have not. It is important to understand here that these are not claims about facts.

Argumentation in this area is often complex and is based on ethical principles, social norms and individual value conceptions.

Moreover, our value conceptions are part of our identity. As soon as someone attacks our values, we see it as an attack on ourselves. Openness is not on the agenda there. We will defend ourselves "to the hilt".

If we can argue here at all, then only via coherence or contradiction.

Most of the time we will only be able to show (in books, films, documentaries) and not prove argumentatively where we end up with certain values:

• Some values, such as freedom and solidarity, perhaps tend to lead to social harmony, peaceful coexistence and prosperity for all citizens.
• Other values, such as elitism, absolutism and discrimination, perhaps tend to lead to chaos, suffering and misery.

About the effects of certain value systems on a thriving society built on solidarity, one can then argue rationally again.

With people who don't care about the suffering of others, who know no empathy, like racists, slaveholders or absolutists, one cannot argue, or only with great difficulty.

Metaphysical belief and worldview convictions — What fundamentally exists?

These questions are often not (or only partially) empirically decidable.
These beliefs form the foundation of our worldview, of all our convictions, of our maxims of action and thus of our identity.

Here, even more than for simple value questions: These articles of belief are normally not up for discussion. We don't change our worldview like an old T-shirt.

In any case: when we discuss articles of belief, we should proceed with the utmost respect and understanding.

Philosophical forms of belief

Even non-religious people have fundamental metaphysical convictions — consciously or unconsciously.

we believe:

• "Only the material world is real; consciousness and mind are products of physical processes" — Materialism
• "Knowledge stems primarily from experience/observation; without empiricism, claims about the world are speculative." — Empiricism
• "The world is fundamentally mental or dependent on consciousness. Matter exists only as an idea in the mind." — Idealism
• "Only my own consciousness certainly exists; everything else (external world/other persons) is ultimately just content of my perception." — Solipsism
• "Reliable knowledge arises primarily through reason/logic (a priori); experience can deceive and is not the final authority." — Rationalism
• "Many (or all) knowledge claims are uncertain; we should withhold judgments until really good reasons are available." — Skepticism

Spiritual forms of belief

we believe:

• "There are no supernatural beings. (gods, spirits, angels, demons ...)" — Atheism
• "Whether God/gods exist cannot be known (currently/in principle)." — Agnosticism
• "There is one God and he is omnipotent, omniscient and all-good." — Monotheism
• "There are many gods and they act upon the world." — Polytheism
• "Everything is divine. God and world coincide." — Pantheism
• "Spirits and ancestors influence the world." — Shamanism/Animism
• "Everything in the universe is interconnected. Unknown energies act upon us." — New Age

Crises of belief

Great crises can sometimes shake or even overturn such basic convictions, because on the one hand they provide "new information", but above all they change the entire sense of plausibility: what we consider possible, whom or what we trust, and how we interpret suffering and chance.

A classic example is the Lisbon earthquake (1755). In the midst of a religiously shaped culture, a natural disaster struck tens of thousands of people. For many, this made the question of theodicy burning: How can a just, omnipotent and benevolent order allow such a thing?

Philosophically, the event acted like a shock against optimistic worldviews (à la "best of all possible worlds") and strengthened in some people skepticism, deism, naturalism or the demand not to delegate moral and political responsibility to "providence".

Even more radically, man-made catastrophes such as the Holocaust shake us. Here it is not only about natural suffering, but about organized cruelty by people and institutions. This can attack basic assumptions such as "humans are good at their core", "civilization means moral progress", "authorities deserve trust" or (religiously) "God protects the righteous".

For some this leads to a loss of faith, for others to a deep transformation of faith (e.g. less triumphalist, more oriented toward lament and responsibility).

Personal crises have a similar effect (death of loved ones, serious illness, violence, betrayal, loss of home/work, depression). They can destroy implicit basic assumptions such as "the world is fundamentally just", "hard work is rewarded", "such a thing won't happen to me", "I have my life under control" or "people are reliable".

Typical consequences are not only new opinions, but a change of the basic tone: from security to vulnerability; from trust to mistrust; from meaning to a search for meaning.

Important: crises do not prove any metaphysical position. But they can make the "costs" of certain worldviews visible (cognitive dissonance). Crises can break trust in authorities/traditions, and thereby open the space for negative doubt up to cynicism. In the positive case, it can lead to humility, solidarity and a more reflective handling of certainties.

Note

Some beliefs are well-founded and testable (empirical), others are primarily evaluative (normative), still others concern fundamental images of reality (metaphysical) or are an expression of trust.

Knowledge

There was this joke in the former Eastern Bloc:

What is the difference between Christians and Communists?
Christians know that they believe —
Communists believe that they know.

What is the difference between belief and knowledge?

Believing means holding something to be true without being able to prove it. Knowledge, on the other hand, is belief with good reasons — we have evidence, experiences or logical arguments. The transition is fluid: what is belief today can become knowledge tomorrow through new insights.

Belief is fast and practical — we can act without thinking everything through. It gives us orientation and support in uncertain situations.

Knowledge, by contrast, is more reliable and helps us make better decisions. It protects us from errors and makes us more independent of authorities.

How is knowledge usually defined?

The classical definition goes like this:

Definition

Knowledge is justified true belief.

This means: I believe something (belief), it is actually correct (true), and I have good reasons for it (justified). These three conditions must all be met.

A look into history: How did philosophers think about knowledge?

Plato (428—348 BC) distinguished between knowledge (episteme) and opinion (doxa). For him, true knowledge referred to unchangeable ideas — like mathematical truths or absolute justice. Sensory experience was unreliable for him.

Aristotle (384—322 BC) was more practically oriented. He saw knowledge as the result of observation and logical inference. His categories and syllogisms shaped Western thought for centuries.

Edmund Gettier (1927—2021) shook the classical definition of knowledge in 1963 with just three pages. Through clever thought experiments, he showed that one can have justified true beliefs that nevertheless do not constitute knowledge — the famous "Gettier problems".

A Gettier example: You look at the clock and think "It is 2:30 p.m.". The clock indeed shows 2:30, but it stopped yesterday. By coincidence, it really is 2:30. You have a justified true belief — but is that knowledge?

The biggest problem is the question of truth: How do we know whether something is really true? Moreover, we can also be wrong even with good reasons — as the history of science shows. Some philosophers therefore doubt whether "absolute" knowledge is possible at all.

Reasons and justifications

Not all reasons are equal. What counts as a good justification in one area can be completely insufficient in another. Here is an overview of different "standards of justification":

Everyday life: practical reason and plausibility

In everyday life, we have to decide quickly, without perfect information:

• "I'll take the umbrella because it looks cloudy."
  • Reason: I have experience and use a precautionary principle.
  • Standard: "It's enough if it's probable."

• "I trust this mechanic because he was recommended to me by friends."
  • Reason: We are socially networked and have social trust.
  • Standard: "A proven track record in similar situations"

• "I don't believe her, because she has already lied to me twice."
  • Reason: An inductive inference from the past
  • Standard: "Patterns are usually reliable."

Everyday justification is pragmatic: it has to be "good enough" to act on, even if it isn't perfect.

Politics: conflicts of interest and rhetoric

In politics, it is rarely only about truth, but also about power, values and forecasts of the future:

• "We should cut taxes because that stimulates the economy."
  • Reason: Economic theory + ideological presuppositions
  • Problem: Which school of economics? Which priorities?

• "This party is unelectable because it will lead us into war."
  • Reason: Extrapolation from the party platform or the past
  • Problem: Speculation about an uncertain future

• "The people have decided — the majority is right."
  • Reason: Democratic legitimacy
  • Problem: The majority can also be wrong. We often have no idea of the complexity of certain questions.

Political justification mixes rational arguments with values, fears and hopes. Here worldviews collide.

Logic: formal correctness

In logic, only the rules of correct inference count:

• Syllogism: "All humans are mortal. Socrates is a human. Therefore Socrates is mortal."
  • Reason: Logical form
  • Standard: "If the premises are true, the conclusion must be true."

• Modus ponens: "If P, then Q. P is the case. Therefore Q."
  • Reason: Valid rule of inference
  • Standard: Formal validity

Logical justification is independent of content — it only guarantees that the inferences are correct, not that the starting points are true.

Science: empirical testability and reproducibility

Scientific justifications must meet strict standards:

• "Smoking causes lung cancer."
  • Reason: Long-term studies, statistics, biological mechanisms
  • Standard: Repeatable experiments, peer review, independent confirmation

• "The Earth is warming due to human CO₂ emissions."
  • Reason: Measurements, models, consensus of the expert community
  • Standard: Convergence of different methods and disciplines

Scientific justification demands objectivity, measurability and the willingness to abandon theories in the face of contradicting evidence.

Some populists criticize science as if it wanted to present itself as an "uncriticizable eternal truth". But that is exactly wrong. Science thrives on critical questioning and constant verification.

As we will see later: Scientific statements and theories must be falsifiable in principle.

Art and literature: aesthetic and emotional justifications

In art, different standards apply:

• "This painting lets us recognize the true beauty of nature."
  • Reason: Aesthetic experience, technical mastery, cultural significance
  • Standard: Subjectivity is legitimate, but not arbitrary

• "This novel brings the true substance of human freedom before our eyes." "Whoever dares to stride through the realm of dreams arrives at truth" E. T. A. Hoffmann

• "This music moves me to tears."
  • Reason: Emotional resonance
  • Standard: Authentic personal experience

Aesthetic justification is more subjective, but not irrational — it is based on experience, tradition and shared cultural codes.

The humanities: interpretation and historical contextualization

Here it is about understanding, not just explaining:

• "Goethe's Faust reflects the crisis of the Enlightenment."
  • Reason: Text analysis, historical context, philosophical parallels
  • Standard: Plausible interpretation with textual evidence and knowledge of the historical background.

• "The French Revolution was inevitable."
  • Reason: Social tensions, economic crises, history of ideas
  • Standard: Coherent narrative with historical sources
  • Here one should not stress the "inevitable" too strongly, because we are in a socio-historical context and not in Newtonian mechanics

Justification in the humanities combines empirical research with interpretive reading — it is less "proving" than "making plausible".

Philosophy: rational argumentation and conceptual clarity

Philosophical justification works with concepts, arguments and thought experiments.

It is a critique of judgment, concept formation and language:

• "Consciousness is more than just brain activity."
  • Reason: Phenomenology, thought experiments (qualia, zombies)
  • Standard: Conceptual coherence, logical consistency

• "Morality is not relative."
  • Reason: Universal principles, rational justifiability
  • Standard: Freedom from contradiction, capacity to command general assent

• "Truth wants no gods beside it." (Nietzsche)
  • Reason: Bird's-eye view, considerations from the history of philosophy
  • Standard: Plausibility

Philosophical justification seeks to convince purely rationally through a critique of reason — but often different, equally rational positions remain.

Conclusion

Depending on the context, different standards apply for good reasons:

• Everyday life: practical and life-serving
• Politics: power-conscious and value-oriented
• Logic: formally correct
• Science: empirically testable
• Art: aesthetically experienceable
• Humanities: interpretively plausible
• Philosophy: rationally justifiable

The art lies in recognizing the appropriate standard in each case and not confusing different domains.

Truth and certainty

How is truth defined?

The question of truth has occupied philosophers for millennia. There are various theories of truth:

Correspondence theory: A statement is true if it corresponds with reality.

• "It is raining" is true if it is actually raining.
• Problem: How can we grasp "reality" independently of our perception?

Coherence theory: A statement is true if it is consistent with our entire system of beliefs.

• "The Earth is round" fits with all other astronomical, physical and geographical findings.
• Problem: A consistent system can nevertheless be false.

Consensus theory: A statement is true if rationally acting persons would agree under ideal conditions.

• "Torture is wrong" could be such a rational consensus.
• Problem: What are "ideal conditions" and who determines them?

Pragmatic theory of truth: A statement is true if it proves itself in practice.

• "This medicine helps" is true if it actually heals.
• Problem: Practical success does not guarantee truth (sometimes placebos work).

The diversity of truths

Just as with justifications, there are different kinds of truth:

Empirical truths: Verifiable through observation

• "Water boils at 100°C (at sea level)"
• Standard: Measurability, reproducibility

Logical/mathematical truths: Recognizable through reason

• "2 + 2 = 4" or "All bachelors are unmarried"
• Standard: Logical necessity, freedom from contradiction

Moral truths: (if they exist)

• "Torturing the innocent is wrong"
• Standard: Capacity to command universal assent? Intuition? Consequences?

Aesthetic truths: Subjective, but not arbitrary

• "This symphony is beautiful"
• Standard: Aesthetic experience, cultural codes

Existential truths: Personal life experiences

• "Life has meaning" or "I am loved"
• Standard: Authentic self-experience, biographical coherence

Are there absolute truths? Different answers

Dogmatism: "Yes, and I know them. I am quite certain."

• Some religious or ideological positions claim absolute certainty.
• Problem: How do I distinguish genuine from supposed certainty?
• Absolute certainty cannot be corrected; one no longer listens

Relativism: "No, truth is always relative to culture/person/time."

• "What is true for you need not be true for me."
• Problem: Is this statement, too, only relatively true? Self-contradiction?

Skepticism: "We can never know for certain what is true."

• Since we can always be wrong, we should make no final claims to truth.
• Problem: Does it render discussion and science pointless?

Fallibilism: "There is truth, but our knowledge is always correctable."

• We strive for truth, but must remain ready to revise our convictions.
• This is the position of most scientists and critical thinkers.

Critical realism: "Reality exists independently of us, but our access to it is limited."

• There are objective truths, but we recognize them only gradually and incompletely.
• Scientific progress is an approximation to truth, not its possession.

The certainty trap

Absolute certainty is humanly impossible — and that is a good thing.
Certainty makes us unteachable and fanatical.
Critical openness, by contrast, makes us capable of learning.

The most important insight: Even though we can never have absolute certainty, not all opinions are equally well-founded.
There are better and worse reasons, even if none are perfect.

Practical consequences

For our life this means:

1. Humility: We can be wrong, even about our strongest convictions.
2. Discernment: Some claims are nevertheless much more probable than others.
3. Openness: We should remain ready to be convinced by better arguments.
4. Responsibility: Even without absolute certainty, we must and can act and decide.

The philosopher Karl Popper put it in a nutshell: "I may be wrong and you may be right, and by an effort, we may get nearer to the truth."

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Footnotes

1. The philosopher Wittgenstein loved such thought experiments. Can we imagine a world in which a meter stick expands as we move from one end of the field to the other? Not very practical, but perhaps amusing. ↩

2. Edward Bernays (1891—1995), an early PR and propaganda pioneer. In 1929 he organized a media campaign in the USA ("Torches of Freedom"), in which women publicly smoked cigarettes in order to frame smoking as a symbol of female emancipation. This was less an expression of real liberation than a deliberate marketing strategy (among other things in the interest of the tobacco industry, who would have thought 🤣). ↩

3. Intellectuals have always been annoying. Socrates was promptly sentenced to death for "corrupting the youth".
   In Nazi Germany, intellectuals were defamed as "degenerate", "un-German", "Jewish-Bolshevist" and generally as "enemies of the people". Their books were burned, they were expelled, persecuted to the point of physical extermination.
   In China under Mao Zedong (Cultural Revolution, 1966—1976), intellectuals were persecuted, humiliated and also physically abused. Intellectuals had to publicly renounce their "hostile" views. ("self-criticism")
   In the USA under Trump, there is a massive attack on intellectuals. Intellectuals and experts are defamed as "elites" or "out of touch" (e.g. in the rhetoric of Donald Trump or parts of the right-wing media).
   There are attacks on the sciences: climate research, gender studies or critical race theory are attacked as "politically motivated" or "un-American".
   We see attempts at censorship: book bans in schools (e.g. in Florida or Texas), restriction of academic freedom. ↩

4. This consensus now stands at over 99% of actively publishing climate scientists. In the strict scientific sense, there is no recognized research organization that disputes human-made climate change as a whole. There are, of course, political-economic think tanks, such as the Heartland Institute (USA) or EIKE (European Institute for Climate and Energy, Germany), which are often cited. These institutes do not conduct their own open-ended research, but are mostly politically motivated or financed by industry money (e.g. from the coal and oil sector). Their "studies" generally do not withstand scientific peer review in specialist journals. ↩

5. The full article reads: "Article 1 (Freedom, Equality, Solidarity)
   All human beings are born free and equal in dignity and rights. They are endowed with reason and conscience and should encounter one another in a spirit of solidarity." Amnesty International — The Universal Declaration of Human Rights: Your rights at a glance UN Declaration of Human Rights
   Classical precursors of this declaration of human rights are the Virginia Declaration of Rights of 1776, and the French Declaration of the Rights of Man and of the Citizen. ↩