''Ab initio'' ( ) is a Latin term meaning "from the beginning" and is derived from the Latin ''ab'' ("from") + ''initio'', ablative singular of ''initium'' ("beginning").


, from Latin, , from ablative case of ''initium'' "entrance, beginning", related to verb ''inire'' "to go into, enter upon, begin".


''Ab initio'' (abbreviation: ''ab init.'') is used in several contexts, including the following:


In law, ''ab initio'' refers to something being the case from the start or from the instant of the act rather than from when the court declared it so. For instance, the term "void ''ab initio''" means "to be treated as invalid from the outset." E.g., in many jurisdictions, if a person signs a contract under duress, that contract is treated as being "void ''ab initio''". Typically, documents or acts which are void ''ab initio'' cannot be fixed and if a jurisdiction, a document or an act is so declared at law to be void ''ab initio'', the parties are returned to their respective positions that they were at the beginning of the event. "Void ''ab initio''" is often contrasted with "voidable", such documents which become void only as of the date of the judicial declaration to that effect. An insurer facing a claim from an insured who had deceived the insurer on a material fact would claim that the insurance contract was void ''ab initio''; it was null and void from the beginning and that since there was no legally enforceable contract, the insurer ought not to have to pay.

Science and engineering

In general, a calculation is said to be ''ab initio'' (or "from first principles") if it relies on basic and established laws of nature without additional assumptions or special models. For example, an ''ab initio'' calculation of the properties of liquid water might start with the properties of the constituent hydrogen and oxygen atoms and the laws of electrostatics and quantum mechanics. From these basics, the properties of isolated individual water molecules would be derived, followed by computations of the interactions of larger and larger groups of water molecules, until the bulk properties of water had been determined. *Documentation of a process is said to be ''ab initio'' (or ''from scratch'', or ''from the ground up'') if the documentation shows how to set up and complete the process from basic materials (to which a competent practitioner is expected to have access) without prior special preparation. * In nuclear physics, the mass-energy of different nuclei can be determined with ''ab initio'' methods by solving the Schrödinger equation over all particles. * Likewise in chemistry, this refers to ''ab initio'' quantum chemistry methods. * In biophysics, this refers to a method for the prediction of protein structures in protein folding. * In bioinformatics, ''ab initio'' (or ''de novo'') methods make predictions about biological features using only a computational model without extrinsic comparison to existing data. * In aviation, this refers to the first stage of flight training.

Other uses

* In literature, a story told ''ab initio'' is told from the beginning. This is as opposed to ''in medias res'' (in the middle of the story). * In learning a subject or foreign language, ''ab initio'' refers to study without previous knowledge or assumptions.

See also

* Abatement ''ab initio'' * ''Ad fontes'' * List of legal Latin terms


External links

Definition at Dictionary.com
Category:Latin legal terminology Category:Latin literary phrases Category:Narrative techniques