Charles Sanders Peirce in the context of "Semiotic elements and classes of signs"

Semiotics is the study of signs. It is an interdisciplinary field that examines what signs are, how they form sign systems, and how individuals use them to communicate meaning. Its main branches are syntactics, which addresses formal relations between signs, semantics, which addresses the relation between signs and their meanings, and pragmatics, which addresses the relation between signs and their users. Semiotics is related to linguistics but has a broader scope that includes nonlinguistic signs, such as maps and clothing.

Signs are entities that stand for something else, like the word cat, which stands for a carnivorous mammal. They can take many forms, such as sounds, images, written marks, and gestures. Iconic signs operate through similarity. For them, the sign vehicle resembles the referent, such as a portrait of a person. Indexical signs are based on a direct physical link, such as smoke as a sign of fire. For symbolic signs, the relation between sign vehicle and referent is conventional or arbitrary, which applies to most linguistic signs. Models of signs analyze the basic components of signs. Ferdinand de Saussure's dyadic model identifies a perceptible image and a concept as the core elements, whereas Charles Sanders Peirce's triadic model distinguishes a sign vehicle, a referent, and an effect in the interpreter's mind.

Abductive reasoning (also called abduction, abductive inference, or retroduction) is a form of logical inference that seeks the simplest and most likely conclusion from a set of observations. It was formulated and advanced by the American philosopher and logician Charles Sanders Peirce beginning in the latter half of the 19th century.

Abductive reasoning, unlike deductive reasoning, yields a plausible conclusion but does not definitively verify it. Abductive conclusions do not eliminate uncertainty or doubt, which is expressed in terms such as "best available" or "most likely". While inductive reasoning draws general conclusions that apply to many situations, abductive conclusions are confined to the particular observations in question.

Originally, fallibilism (from Medieval Latin: fallibilis, "liable to error") is the philosophical principle that propositions can be accepted even though they cannot be conclusively proven or justified, or that neither knowledge nor belief is certain. The term was coined in the late nineteenth century by the American philosopher Charles Sanders Peirce, as a response to foundationalism. Theorists, following Austrian-British philosopher Karl Popper, may also refer to fallibilism as the notion that knowledge might turn out to be false. Furthermore, fallibilism is said to imply corrigibilism, the principle that propositions are open to revision. Fallibilism is often juxtaposed with infallibilism.

In semiotics, a sign is anything that communicates a meaning that is not the sign itself to the interpreter of the sign. The meaning can be intentional, as when a word is uttered with a specific meaning, or unintentional, as when a symptom is taken as a sign of a particular medical condition. Signs can communicate through any of the senses, visual, auditory, tactile, olfactory, or taste.

Two major theories describe the way signs acquire the ability to transfer information. Both theories understand the defining property of the sign as a relation between a number of elements. In semiology, the tradition of semiotics developed by Ferdinand de Saussure (1857–1913), the sign relation is dyadic, consisting only of a form of the sign (the signifier) and its meaning (the signified). Saussure saw this relation as being essentially arbitrary (the principle of semiotic arbitrariness), motivated only by social convention. Saussure's theory has been particularly influential in the study of linguistic signs. The other major semiotic theory, developed by Charles Sanders Peirce (1839–1914), defines the sign as a triadic relation as "something that stands for something, to someone in some capacity". This means that a sign is a relation between the sign vehicle (the specific physical form of the sign), a sign object (the aspect of the world that the sign carries meaning about) and an interpretant (the meaning of the sign as understood by an interpreter). According to Peirce, signs can be divided by the type of relation that holds the sign relation together as either icons, indices or symbols. Icons are those signs that signify by means of similarity between sign vehicle and sign object (e.g. a portrait or map), indices are those that signify by means of a direct relation of contiguity or causality between sign vehicle and sign object (e.g. a symptom), and symbols are those that signify through a law or arbitrary social convention.

Inferences are steps in logical reasoning, moving from premises to logical consequences; etymologically, the word infer means to "carry forward". Inference is theoretically traditionally divided into deduction and induction, a distinction that in Europe dates at least to Aristotle (300s BC). Deduction is inference deriving logical conclusions from premises known or assumed to be true, with the laws of valid inference being studied in logic. Induction is inference from particular evidence to a universal conclusion. A third type of inference is sometimes distinguished, notably by Charles Sanders Peirce, contradistinguishing abduction from induction.

Various fields study how inference is done in practice. Human inference (i.e. how humans draw conclusions) is traditionally studied within the fields of logic, argumentation studies, and cognitive psychology; artificial intelligence researchers develop automated inference systems to emulate human inference. Statistical inference uses mathematics to draw conclusions in the presence of uncertainty. This generalizes deterministic reasoning, with the absence of uncertainty as a special case. Statistical inference uses quantitative or qualitative (categorical) data which may be subject to random variations.

Verificationism, also known as the verification principle or the verifiability criterion of meaning, is a doctrine in philosophy and the philosophy of language which holds that a declarative sentence is cognitively meaningful only if it is either analytic or tautological (true or false in virtue of its logical form and definitions) or at least in principle verifiable by experience. On this view, many traditional statements of metaphysics, theology, and some of ethics and aesthetics are said to lack truth value or factual content, even though they may still function as expressions of emotions or attitudes rather than as genuine assertions. Verificationism was typically formulated as an empiricist criterion of cognitive significance: a proposed test for distinguishing meaningful, truth-apt sentences from "nonsense".

As a self-conscious movement, verificationism was a central thesis of logical positivism (or logical empiricism), developed in the 1920s and 1930s by members of the Vienna Circle and their allies in early analytic philosophy. Drawing on earlier empiricism and positivism (especially David Hume, Auguste Comte and Ernst Mach), on pragmatism (notably C. S. Peirce and William James), and on the logical and semantic innovations of Gottlob Frege and the early Wittgenstein, these philosophers sought a "scientific" conception of philosophy in which meaningful discourse would either consist in empirical claims ultimately testable by observation or in analytic truths of logic and mathematics. The verification principle was intended to explain why many traditional metaphysical disputes seemed irresolvable, to demarcate science from pseudo-science and speculative metaphysics, and to vindicate the special status of the natural sciences by taking empirical testability as the paradigm of serious inquiry.

In semiotics, a modality is a particular way in which information is to be encoded for presentation to humans, i.e. to the type of sign and to the status of reality ascribed to or claimed by a sign, text, or genre. It is more closely associated with the semiotics of Charles Peirce (1839–1914) than Ferdinand de Saussure (1857–1913) because meaning is conceived as an effect of a set of signs. In the Peircean model, a reference is made to an object when the sign (or representamen) is interpreted recursively by another sign (which becomes its interpretant), a conception of meaning that does in fact imply a classification of sign types.

Pragmatism is a philosophical tradition that views language and thought as tools for prediction, problem solving, and action, rather than describing, representing, or mirroring reality. Pragmatists contend that most philosophical topics—such as the nature of knowledge, language, concepts, meaning, belief, and science—are best viewed in terms of their practical uses and successes.

Pragmatism began in the United States in the 1870s. Its origins are often attributed to philosophers Charles Sanders Peirce, William James and John Dewey. In 1878, Peirce described it in his pragmatic maxim: "Consider the practical effects of the objects of your conception. Then, your conception of those effects is the whole of your conception of the object."

Ferdinand Mongin de Saussure (/soʊˈsjʊər/; French: [fɛʁdinɑ̃ də sosyʁ]; 26 November 1857 – 22 February 1913) was a Swiss linguist, semiotician and philosopher. His ideas laid a foundation for many significant developments in both linguistics and semiotics in the 20th century. He is widely considered one of the founders of 20th-century linguistics and one of two major founders (together with Charles Sanders Peirce) of semiotics, or semiology, as Saussure called it.

One of his translators, Roy Harris, summarized Saussure's contribution to linguistics and the study of "the whole range of human sciences. It is particularly marked in linguistics, philosophy, psychoanalysis, psychology, sociology and anthropology." Although they have undergone extension and critique over time, the dimensions of organization introduced by Saussure continue to inform contemporary approaches to the phenomenon of language. As Leonard Bloomfield stated after reviewing Saussure's work: "he has given us the theoretical basis for a science of human speech".