What does it really mean to know something? And when we say something is true, what exactly are we claiming? These questions may sound simple, but they sit at the very core of philosophical inquiry. Truth and knowledge are not single, uniform concepts – they carry layers of meaning across different domains of human thought. Whether we are examining a scientific claim, a moral judgment, or a statement about the nature of reality itself, the standards we use to assess truth shift in significant ways. Understanding these shifts – and why certainty remains so difficult to achieve – is one of the most important and enduring challenges in philosophy.
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What truth and knowledge really mean
At first glance, truth seems straightforward: a statement is true if it corresponds to reality. Knowledge appears equally simple: we know something if we believe it and it is true. But philosophy is never quite that tidy. The classical account, widely associated with Plato and discussed extensively in dialogues like Meno and Theaetetus, defines knowledge as justified true belief (JTB). This means three conditions must hold: a person must believe a proposition, the proposition must actually be true, and the person must have adequate justification – that is, good reasons or evidence – for holding that belief.
This framework is intuitive because it rules out lucky guesses. Suppose you believe it will rain tomorrow and it does, but only because you read a fortune cookie. You got it right, but most people would hesitate to say you knew it would rain. The fact that a belief is true does not automatically tell us whether it is justified; that depends on how the belief was arrived at. Justification is the crucial bridge between mere belief and genuine knowledge. It answers the question: why should this belief be trusted rather than dismissed as coincidence?
The Gettier problem: when JTB falls short
The JTB account dominated epistemology for centuries – until 1963, when philosopher Edmund Gettier published a short but landmark paper showing it was incomplete. Gettier-type counterexamples challenge the JTB account by showing that a person can have a justified true belief and still fail to know the proposition, because the justification and the truth are only accidentally connected. The classic example involves a person who believes the time is correct based on a clock that, unknown to them, stopped exactly twelve hours ago. The belief is true and justified – but still not quite knowledge. A lesson of the Gettier problem is that even justified true beliefs can be epistemically lucky in a way inconsistent with genuine knowledge. Philosophers have since proposed adding further conditions – reliability, the absence of defeaters, or virtue-based accounts – to patch the gap.
Three types of truth: epistemological, moral, and ontological
Not all truth claims are created equal. Philosophers distinguish between at least three broad categories of truth, each raising its own distinct challenges for knowledge and certainty.
Epistemological truth
Epistemological truth is truth about knowledge itself – whether a belief or claim accurately reflects what we can know about the world. This is the domain most directly tied to the JTB framework and its revisions. Epistemology examines the nature and types of knowledge, its sources like perception, inference, and testimony, and what people can and cannot know. The central question here is not just whether something is true, but whether we can be justified in believing it to be true given the cognitive tools available to us. Scientific truths, logical truths, and mathematical truths are primary examples – claims that are verifiable, repeatable, and grounded in methods designed to track reality as accurately as possible.
Moral truth
Moral truth is considerably more contested. Moral epistemology asks whether we can ever know, or at least have some justification for believing, whether anything is morally right or wrong, just or unjust. Unlike scientific truths, we cannot simply run an experiment to confirm that honesty is a virtue or that cruelty is wrong. We do not perceive moral truth the way we perceive physical objects, nor do we deduce it with the certainty of mathematics.
The major positions in this debate reflect deep disagreement. Moral realism holds that moral statements can be true or false, while error theory claims that all moral judgments are false because there are no moral truths, and ethical subjectivism suggests that only some moral statements carry a truth value. Deontologists like Kant argue that moral truths are objective and universal, grounded in reason. Moral relativists, on the other hand, contend that moral truths are relative to the social group or cultural context in which they arise. This diversity of moral frameworks across cultures raises a serious challenge: if moral truths were truly universal and knowable, why do thoughtful people across societies so persistently disagree about them?
The entry in moral epistemology assumes that moral knowledge entails roughly justified true moral belief – the same basic structure as ordinary knowledge. But the difficulty of identifying what would count as evidence for a moral claim, and the intrinsically motivating character of moral judgment, make this a uniquely difficult domain. Moral knowledge, if it exists, appears to require a combination of ethical reasoning, cultural sensitivity, and philosophical reflection that goes well beyond what empirical observation alone can supply.
Ontological truth
Ontological truth concerns what actually exists – the nature of being and reality itself. Ontology is concerned with what actually exists in the world about which humans can acquire knowledge, and helps researchers recognize how certain they can be about the nature and existence of objects they are researching. Ontological questions include: Does the external world exist independently of our perception of it? Are abstract entities like numbers real? What is the relationship between mind and matter?
Realist ontology asserts the existence of one single reality that can be studied and experienced as truth, while relativist ontology holds that reality is constructed within the human mind, meaning no single “true” reality exists. These are not merely academic disagreements. They have direct consequences for how we understand the limits of human knowledge. If reality exists independently of our minds, then our knowledge claims are answerable to something beyond us. If reality is partly or wholly mind-dependent, then the idea of a fixed, objective truth becomes far more complicated.
Evidence as the criterion for truth
Across all three domains, evidence plays a central role in determining what we should believe. In epistemology, evidence is often taken to be relevant to justified belief, where the latter is typically thought to be necessary for knowledge. Without evidence, a belief remains mere opinion or speculation – something we might hold, but cannot reasonably claim to know.
In the sciences, this relationship is clearest. Hypotheses are tested against observable data, and the weight of evidence determines which theories are accepted or revised. The laws of physics, for instance, are not simply declared true – they are confirmed through repeated, independent experiments. But there is no more pervasive problem in epistemology than the underdetermination of theory by evidence – the recognition that the same body of evidence can often support multiple competing theories. Two scientists examining identical data may reach different conclusions based on background assumptions, theoretical commitments, or interpretive frameworks.
The evidentialist view in epistemology holds that we ought to believe in accord with our evidence. But even this seemingly reasonable standard raises hard questions. What counts as evidence? How much evidence is enough? And how do we account for cognitive biases – like confirmation bias – that shape which evidence we notice and how we interpret it?
Why certainty remains elusive
Given all of this, it should come as no surprise that achieving certainty in knowledge is extraordinarily difficult. Philosophers have disagreed sharply about the complex relationship between the concepts of knowledge and certainty – whether they are the same, how they differ, and whether it is possible to know something without being certain of it.
One important distinction is between psychological certainty – the subjective feeling of being sure – and epistemic certainty – the objective property of a proposition being guaranteed true by the available evidence. Feeling certain about something does not make it epistemologically certain. History is full of examples of beliefs held with absolute conviction that turned out to be false: geocentrism, the luminiferous ether, and countless medical treatments once considered established are now discarded. Epistemic certainty requires that one’s justification be infallible – an extraordinarily high standard that few, if any, of our ordinary beliefs can meet.
Philosophical skepticism takes this further. Moral skeptics challenge the existence of moral knowledge, metaphysical skeptics say humans cannot know ultimate reality, and global skepticism asserts that there is no knowledge in any domain. Few philosophers defend global skepticism outright, but the skeptical challenge has been enormously productive: it forces us to examine, rigorously and honestly, what the actual grounds of our knowledge claims are. René Descartes famously attempted to defeat skepticism by doubting everything he could possibly doubt, arriving at the one proposition he could not doubt – that he was thinking. From this he tried to rebuild a secure foundation for knowledge. The project remains controversial, but it illustrates how seriously the problem of certainty has been taken.
Fallibilism offers a more pragmatic response. Rather than demanding certainty, fallibilism holds that claims can be accepted even though they cannot be conclusively proven or justified. Knowledge, on this view, is not a fixed achievement but a revisable approximation – the best we can do given current evidence and reasoning, always open to correction in light of new information. This is arguably the attitude that underlies modern scientific practice: we accept the best-supported theories while remaining open to revision. It is a humbler but perhaps more honest relationship with truth.
The broader implications
The distinctions between epistemological, moral, and ontological truth are not merely academic. They structure the way we reason about science, ethics, and the nature of reality in practical, everyday ways. When a government debates public health policy, it draws on epistemological truth – the best available scientific evidence. When it debates justice or rights, it engages with moral truth – contested, culturally embedded, and resistant to simple verification. And underlying both is an ontological commitment to what kind of world we take ourselves to be living in.
The concept of evidence, meanwhile, is the thread that ties knowledge across these domains together. In the philosophy of science, evidence is what confirms or refutes scientific theories, constituting the grounds for rationally deciding between competing pictures of the world. But as we move from science to ethics to metaphysics, the nature of evidence changes – and so does our confidence in the resulting knowledge. Recognizing these differences is not a counsel of despair. It is an invitation to think more carefully about what we are really claiming when we say we know something, and what kind of truth we are reaching for.
What do you think? If certainty is unattainable in most areas of knowledge, does that mean we should treat scientific truths and moral truths as equally uncertain – or are there meaningful differences in how confidently we can hold beliefs in each domain? And when two people look at the same evidence and reach opposite conclusions, what does that tell us about the relationship between evidence and truth?
References
- https://plato.stanford.edu/entries/epistemology/
- https://iep.utm.edu/epistemo/
- https://en.wikipedia.org/wiki/Gettier_problem
- https://plato.stanford.edu/entries/knowledge-analysis/
- https://en.wikipedia.org/wiki/Epistemology
- https://iep.utm.edu/mor-epis/
- https://www.ebsco.com/research-starters/religion-and-philosophy/metaethics
- https://plato.stanford.edu/entries/moral-epistemology/
- https://i2insights.org/2017/05/02/philosophy-for-interdisciplinarity/
- https://iep.utm.edu/evidence/
- https://www.britannica.com/topic/epistemology/Knowledge-and-certainty
- https://iep.utm.edu/certainty/
- https://en.wikipedia.org/wiki/Justification_(epistemology)
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