{{wiktionary|formal|informal}}
'''Formal''', '''formality''', '''informal''' or '''informality''' imply the complying with, or not complying with, some set of requirements (forms, in Ancient Greek). They may refer to: {{TOC right}}
==Dress code and events== * Formal wear, attire for formal events * Semi-formal attire, attire for semi-formal events * Informal attire, more controlled attire than casual but less than formal * Formal (university), official university dinner, ball or other event * School formal, official school dinner, ball or other event
==Logic and mathematics== *Formal logic, or symbolic logic ** Informal logic, the complement, whose definition and scope is contentious *Formal fallacy, reasoning of invalid structure ** Informal fallacy, the complement *Informal mathematics, also called naïve mathematics *Formal cause, Aristotle's intrinsic, determining cause *Formal power series, a generalization of power series without requiring convergence, used in combinatorics *Formal calculation, a calculation which is systematic, but without a rigorous justification *Formal set theory, as opposed to Naive set theory<!--second blue link appropriate here to explain "formal" in this context --> *Formal derivative, an operation on elements of a polynomial ring which mimics the form of the derivative from calculus
==Computer science== *Formal methods, mathematically based techniques for the specification, development and verification of software and hardware systems *Formal specification, describes what a system should do, not how it should do it *Formal verification, proves correctness of a system
==Linguistics== *Formal system, an abstract means of generating inferences in a formal language *Formal language, comprising the symbolic "words" or "sentences" of a formal system *Formal grammar, a grammar describing a formal language *Colloquialism, the linguistic style used for informal communication *T–V distinction, involving a distinction between formal and informal words for "you" *Formal proof, a fully rigorous proof as is possible only in a formal system *Dynamic and formal equivalence word-for-word translation, especially of the Bible
==Chemistry== *Formal concentration, molar concentration of original chemical formula in solution *Formal (pronounced "form-al") **A compound CH<sub>2</sub>(OR)<sub>2</sub>, named in analogy to acetals CHR<sup>1</sup>(OR)<sub>2</sub> (historical definition) and ketals CR<sup>1</sup>R<sup>2</sup>(OR)<sub>2</sub> **Dimethoxymethane (CH<sub>2</sub>(OCH<sub>3</sub>)<sub>2</sub>) in particular, the formal derived from methanol
==Social regulation== * A formality, an established procedure or set of specific behaviors ** Pro forma, for no purpose other than satisfying a formality *Informal activities: ** Informal education, education outside of a standard school setting ** Informal sector, the part of an economy that is not taxed, nor monitored by any form of government ** Informal settlement, or shanty town ** Informal value transfer system, outside the conventional banking system ** Informal social control, enforcing norms without resort to laws
==Other== * Informal vote, a spoiled, void, null vote cast in an election * MV ''Formality'', coaster (formerly ''Empire Favourite'') owned by F T Everard & Sons, scrapped in 1962
==See also== * Form (disambiguation) * Formalism (disambiguation) * Formal theory (disambiguation)
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