Say the ratio out loud before you open Reasoning — recalling it unprompted is exactly what the exam pays for.
Why it matters
It decides when formal validity is tested, and it establishes the asymmetry that governs the head: a good marriage cannot be destroyed by later legislation, but a bad one can be cured by it.
Facts
Two Polish-domiciled Roman Catholics married in an Austrian church in May 1947 with no civil ceremony, which the lex loci then required. Austrian legislation validated such marriages retrospectively a few weeks later. The marriage was registered in 1949, by which time the parties were domiciled in England. In 1950 the wife went through a second marriage in England.
Held
The Austrian marriage was good, having been validated retrospectively by the lex loci. The second English marriage was therefore bigamous and void.
Reasoning
Step one — the first limb of the timing rule. The lex loci at the time of celebration determines formal validity once for all, and the married status is unaffected by changes introduced subsequently; otherwise the relationship between the parties would remain insecure.
Step two — the second limb. A marriage which does not comply with the formalities prescribed by the lex loci at the time of the marriage may be validated by subsequent retrospective changes in the lex loci.
Step three — why the asymmetry is deliberate. Both limbs serve the same policy, the security of status. A rule letting later legislation destroy a completed marriage would make every marriage provisional. A rule refusing to let later legislation cure a defective one would leave couples unmarried who believe themselves married and whose own legislature has said they are.
Step four — the doctrinal justification. Locus regit actum is a reference to a legal system, not to a snapshot of that system. The forum takes the lex loci as it finds it, including its retrospective operation.
Exam use
It opens: At what time is the formal validity of a marriage judged? — state the asymmetry, then the case.
Show the consequences running on. The parties had changed their domicile to England before registration, and it made no difference: form is for the place of celebration, and the later domicile is irrelevant. The second marriage then failed not for any defect of its own but because the first subsisted.
Pair it with Simonin v. Mallac, which supplies the rule itself and the point that evasion is irrelevant to form, and with Ogden v. Ogden, which shows the classification of the same requirement differing across a frontier and producing a limping marriage.
Remember the exceptions to locus regit actum, because they show that the connecting factor is a servant of its reason: marriages under the statutory provisions for marriages before a marriage officer abroad, marriages of members of the armed forces serving abroad celebrated by a chaplain with the force or the authorised commanding officer, the common law exception where compliance with the lex loci is impossible, and marriages on the high seas.
It does not decide anything about essential validity, which no retrospective legislation of the place of celebration can supply.