Definition of lex causae
In the conflict of laws, lex causae (Latin: lex+causa, "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 regulates all lawsuits involving "foreign" law, where the outcome of a legal action will differ based 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.
When the parties and the causes of action are local, the court will apply the lex fori, the prevailing municipal law. If there are "foreign" elements to the case, the forum court should under the conflict of laws consider whether it should apply one or more foreign laws.
For example, suppose that a woman 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 where 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 under 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 under the lex domicilii, the law of her domicile; 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.
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