# cogency

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**Model theory**— This article is about the mathematical discipline. For the informal notion in other parts of mathematics and science, see Mathematical model. In mathematics, model theory is the study of (classes of) mathematical structures (e.g. groups, fields,… …62

**Class (set theory)**— In set theory and its applications throughout mathematics, a class is a collection of sets (or sometimes other mathematical objects) which can be unambiguously defined by a property that all its members share. The precise definition of class… …63

**Constructivism (mathematics)**— In the philosophy of mathematics, constructivism asserts that it is necessary to find (or construct ) a mathematical object to prove that it exists. When one assumes that an object does not exist and derives a contradiction from that assumption,… …64

**Nominalism**— is a metaphysical view in philosophy according to which general or abstract terms and predicates exist, while universals or abstract objects, which are sometimes thought to correspond to these terms, do not exist.[1] Thus, there are at least two… …65

**Ontology**— This article concerns ontology in philosophy. For the concept in information science, see Ontology (information science). Not to be confused with the medical concepts of oncology and odontology, or indeed ontogeny. Parmenides was among the first… …66

**Ordered pair**— In mathematics, an ordered pair (a, b) is a pair of mathematical objects. In the ordered pair (a, b), the object a is called the first entry, and the object b the second entry of the pair. Alternatively, the objects are called the first and… …67

**Propaganda**— This article is about the form of communication. For other uses, see Propaganda (disambiguation). French Military Propaganda postcard showing a caricature of Kaiser Wilhelm II biting the world (c. 1915) …68

**Paradox**— For other uses, see Paradox (disambiguation). Further information: List of paradoxes A paradox is a seemingly true statement or group of statements that lead to a contradiction or a situation which seems to defy logic or intuition. Typically,… …69

**Rhetoric**— This article is about the art of rhetoric in general. For the work by Aristotle, see Rhetoric (Aristotle). Painting depicting a lecture in a knight academy, painted by Pieter Isaacsz or Reinhold Timm for Rosenborg Castle as part of a series of… …70

**Set (mathematics)**— This article gives an introduction to what mathematicians call intuitive or naive set theory; for a more detailed account see Naive set theory. For a rigorous modern axiomatic treatment of sets, see Set theory. The intersection of two sets is… …