In the conflict of laws
, lex causae
, "cause [for the] law") is the law or laws chosen by the forum court
from among the relevant legal systems
to arrive at its judgement of an international or interjurisdictional case
The term refers to the usage of particular local
laws as the basis or "cause" for the ruling, which would itself become part of referenced legal canon.
Conflict of laws is the branch of public law which regulates all lawsuits involving a "foreign" law element, where a difference in result will occur depending on which laws are applied.
Once the forum court has ruled that it has jurisdiction to hear the case, it must then decide which of the possible laws are to be applied to resolve the dispute.
When a case comes before a court and all the main features of the case are local, the court will apply the lex fori
, the prevailing municipal law
, to decide the case. But if there are "foreign" elements to the case, the forum court may be obliged under the Conflict of Laws system to consider whether it should apply one or more foreign laws to decide the case. This is a two stage process:
- it must first characterise the issues, i.e. allocate the factual basis of the case to its relevant legal classes; and
- then apply the choice of law rules to decide which law is to be applied to each class.
For example, suppose that a person domiciled in Scotland and a person habitually resident in France, both being of the Islamic faith, go through an Islamic form of marriage in Egypt while on holiday. This ceremony is not registered with the Egyptian authorities. They establish a matrimonial home in Algeria where they buy a house in the husband's name. The relationship breaks down and the wife returns to Scotland. When she hears that the husband is proposing to sell the house, she goes to the courts in Scotland. Is this:
- a case involving title to land in which case the choice of law rule is that the lex situs, the law of the place where the land is situated, will be applied;
- a case to decide whether the Egyptian ceremony created a valid marriage which will usually be determined by reference to the ''lex loci celebrationis, the law of the place where the marriage was celebrated;
- a case to decide whether she has the status of a wife and so may seek matrimonial relief in which case the choice of law rule is that the lex domicilii, the law of her domicile, applies; or
- a case to seek divorce in which case the lex fori substantive Family Law will apply?
Assuming that the three relevant laws (the domicile and the forum is in Scotland) would give different results, the choice of the lex causae assumes major significance (see also incidental question).