What is meant by ab initio?
when describing literature: told from the beginning as opposed to in medias res (meaning starting in the middle of the story)
as a legal term: 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. A judicial declaration of the invalidity of a marriage ab initio is a nullity.
in science: 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 electrodynamics. 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 ...more