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."
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.
[3] 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.
This in contrast to an approach that uses approximations (which could allow for easier computations) that have no direct link to these first principles.