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:
Dress code and events
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
- 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
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
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