In france, there's a thing called the law-screen theory which states that a judge only applies the law, and not the constitution. If someone says they're being tried unconstitutionally, they can claim the law they are opposed is unconstitutional, raise what's called a priority constitutional question which is adjudicated by a special body, the constitutional council, not considered part of the judicial system.

I know this is not the case in the US because the SCOTUS adjudicates both statutes and the constitution, but do all (federal) court work this way, applying both the law and the constitution ?

I would also (but less) be interested in how that works at the state level, particularly in Louisiana which applies some of the Civil law legal system, akin to the french judicial system.

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Every court in the United States from municipal traffic court to a state court to a U.S. District Court has both the right and the obligation to consider claims of unconstitutionality just like any other legal question that a case presents. Contrary to popular misconception, constitutional law issues are not the exclusive province of the U.S. Supreme Court. Indeed, constitutional issues are only ruled upon in the first instance in the U.S. Supreme Court (or even in a direct appeal from a trial court to the U.S. Supreme Court) in rare and isolated cases. Usually, at least one trial court judge and at least three appellate court judges, and often more appellate court judges, have ruled upon a constitutional issue before the U.S. Supreme Court considers it.

This is just as true in Louisiana and Puerto Rico, which have legal systems based upon the civil law legal system, as it is in other U.S. jurisdictions, which have a common law legal system.

There is usually only one difference between a case in which the constitutionality of a statute is called into question and one in which it is not. When the constitutionality of a statute is called into question, many state and federal rules of civil procedure require or permit the attorney general of the state whose statute's constitutionality (or the U.S. attorney general when a federal law's constitutionality is at issue) to be joined as a party for the purpose of litigating that issue. This allows the court to receive arguments on the constitutional issue from the public's perspective as well as the perspectives of the parties.

A few states also provide that appeals from trial court decisions finding that a statute is unconstitutional are directly to the state supreme court, rather than to the intermediate court of appeals as they would usually be in those states.

Notably, the distinct treatment of constitutional issues in many civil law systems is not inherently a part of the civil law system. Constitutional courts are mostly a post-World War II constitutional innovation in the countries where they are found.

For example, the "law-screen" doctrine and the existence of a constitutional court in France, is much younger than core of the rest of the civil law system in France, which invented the civil law system in its modern form more than two hundred years ago. Neither France, at the time Louisiana adopted its civil law legal system through the time of the Louisiana Purchase, nor Spain at the time that Puerto Rico was ceded to the United States after the Spanish-American war, had constitutional courts.

Footnote Regarding Treaties

Also, it is worth remarking that in Europe and much of the rest of the world, the function of protecting individual rights against government authority in a way that is entrenched so that it is not easily overcome by domestic legislation of a current political regime is accomplished through international treaties, rather than only through entrenched rights in a constitution as they are in the United States. Although even then, in many European countries, ordinary courts apply only domestic law and the country in question has to adopt domestic law to conform to the treaties.

This treaty mechanism is not very effective in the U.S., because in the U.S., unlike most countries, an ordinary domestic law can override an earlier adopted and ratified international treaty.

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    One additional footnote that should be pointed out is that at least three common law nations do not have codified constitutions (The U.K. and New Zealand have never made any attempts to draft one, while Israel has attempted to draft a Constitution, but has never been able to ratify one.).
    – hszmv
    Dec 9, 2022 at 18:03
  • @hszmv In the same vein, Canada didn't have a true, entrenched, constitution until 1982.
    – ohwilleke
    Dec 9, 2022 at 18:06
  • Yeah, I was aware they have one now and that it was relatively recent. In general, I've always found the answer to "When did Canada become an Independent Country?" to be a bit difficult to actually pin, given their ties to the British/U.K. being much more lasting than U.S. Independence (and a hell of a lot less interesting).
    – hszmv
    Dec 9, 2022 at 18:12
  • @hszmv IIRC, Canadian independence dates to 1867.
    – ohwilleke
    Dec 9, 2022 at 20:37
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    @hszmv, ohwilleke: from 1867 until the statute of Westminster in 1931, Canada was still subject to the legislative authority of the UK parliament, and until 1982 Canada's constitution remained under control of the the UK parliament, so it is indeed difficult to identify a point in time at which Canada became independent -- it happened gradually.
    – phoog
    Dec 10, 2022 at 12:33

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