Truth is central to many disciplines. It is often considered a goal of inquiry that guides scientific research and intellectual life.^[1] Empirical scientists formulate testable hypotheses to explain phenomena. They rely on observation and experimentation to collect objective data, comparing results with initial hypotheses to confirm or disconfirm their theories.^[2] The natural sciences engage in quantitative research, employing precise numerical measurements, often to arrive at exact general laws that can predict future outcomes. Qualitative research is more common in the social sciences, where researchers examine cultural phenomena, social processes, and subjective experiences that may resist purely numerical interpretation.^[3]

The formal sciences demonstrate the truth of theories through more abstract methods, usually based on deductive reasoning.^[4] For example, mathematicians employ several proof methods to establish theorems, such as direct proof, proof by contradiction, and mathematical induction.^[5] Formal logic studies the nature of deductive reasoning and the rules of inference it follows. A key principle in this field is that deductive inferences preserve truth: if all premises are true, then the conclusion cannot be false. Logicians develop formal systems—abstract frameworks that precisely encode forms of deductive reasoning—and examine which truths can and cannot be proven within a given formal system.^[6][a] Truth tables, another tool in logic, express how the truth values of compound propositions depend on those of their constituent propositions.^[8]

Many issues concerning the relation between truth and inquiry are addressed by epistemology, which studies the nature, origins, and limits of knowledge. This field treats truth as a central aspect of knowledge^[b] and examines the ways of attaining it, including the approaches of the empirical and formal sciences.^[10] The philosophy of language and semantics regard truth as an aspect of the meaning of sentences. They are interested in the relation between words, ideas, and the world and analyze phenomena that complicate this relation, such as ambiguity, vagueness, and context dependence. They also address the problem of truth-value gaps: the question of whether some statements are neither true nor false.^[11][c]

Ethics is concerned with right behavior, including truth-related behavior. For example, Immanuel Kant argued that people have a duty to tell the truth and are prohibited from lying. In metaethics, philosophers discuss whether moral statements and principles can be true, as cognitivists claim, or not, as non-cognitivists contend.^[13]

Truth plays a central role in many religions. The Abrahamic traditions stress the importance of truthfulness and closely link truth to the divine, as reflected in the Jewish description of God as El Emet (God of truth), Jesus's statement "I am the way, the truth, and the life" in Christianity, and the Islamic term Al-Haqq (the Truth) as one of Allah's names.^[14] Philosophers in these traditions have debated the relationship between the religious truths of faith and the philosophical truths of reason. They typically argue that apparent tensions are resolvable through right interpretation. An alternative approach relies on the doctrine of double truth, according to which divergent truths can coexist in different domains.^[15]

In Hinduism, truth or satya is a key virtue to be practiced in thought, speech, and action, and is considered a source of individual and societal well-being. For example, it is one of the five moral restraints in Patanjali's Yoga.^[16] In Buddhism, the concept of truth is closely related to Buddha's teachings, such as the doctrine of the Four Noble Truths about the causes of suffering and the path to liberation.^[17] Buddhists also hold the theory of two truths, according to which conventional truth, associated with the phenomenal world and everyday experience, differs from ultimate truth, which concerns the fundamental nature of reality and is required for attaining liberation.^[18] A related contrast in Jainism distinguishes between relative truth, which is limited to a particular time, place, and perspective, and absolute truth, which transcends individual viewpoints but cannot be fully expressed in language.^[19] A form of perspectivism is also found in Taoism, which argues that knowledge is shaped by a person's interests and engagement with the world, with each perspective providing only a partial view of reality.^[20]

Truth can also be expressed in the field of art by manifesting ideas or understanding through aesthetic phenomena. The meanings of artworks are not always directly accessible and may require interpretation to uncover. For example, a novel exploring the feelings and choices of fictional characters may reveal deeper truths about human nature and moral dilemmas. Artworks may also evoke experiences that a person has not felt before, showing them new perspectives, familiarizing them with alternative ways of life, or preparing them for possible future challenges. Aesthetic philosophers discuss whether or how the truths expressed in an artwork shape aesthetic experience and contribute to its overall value.^[21]

Truth plays a central role in law as a guiding norm to which legal processes and decisions should align. Because of difficulties in reconstructing what happened, this field relies on various standards of proof and evidentiary rules to ascertain pertinent facts. Consequently, truth by itself can be insufficient if it cannot be proven in court, contrasting factual truth with legal truth.^[22]

Similarly, truth is a key element in journalism, where reporters seek information from reliable sources and fact-check claims to accurately inform the public. Media theorists discuss obstacles to this process, such as the spread of misinformation, misleadingly edited photographs, AI-generated images, political propaganda, and algorithmic biases on social media platforms.^[23]

Psychologists and cognitive scientists study cognitions as truth-related mental processes that acquire, transform, or use information. They examine different types of cognitive processes, like perception, memory, and thought, and investigate how biases and distortions affect these processes.^[24]

In computer science, true and false are values of constants and variables belonging to the Boolean data type. One of their key applications happens in control structures that determine the flow of code execution, such as conditional expressions that execute a code path only if a test condition evaluates to true.^[25]

Probability theory deals with uncertain information. It uses numbers between 0 and 1 to represent the probability that a statement is true and provides rules for calculating how the probabilities of different statements influence each other.^[26]

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