The Constitution of the United States is the bedrock upon which all laws and governance relies upon for its legality, and we commonly perceive the Supreme Court as the final arbiter of whether a law is sufficiently in keeping with the Constitution. The practice of this determination is commonly referred to as 'judicial review'.
This great power of the Supreme Court was also never explicitly granted to them in the Constitution. Article III only establishes a Supreme Court, it wasn't until Marbury v. Madison in 1803 that Chief Justice John Marshall made the concept part of the American judicial system.
Because the constitutionality of law was then and has since been subject to the judgement of the courts, those on the courts have ultimately created their own interpretations on how to read the Constitution. While it's easy to divide these camps into 'left' and 'right' or 'conservative' and 'liberal', these labels are political in nature and have no real legal meaning. After all, how does one legally define 'liberal', 'libertarian', 'progressive', or 'conservative'? The labels for these interpretations must therefore be derived from how the Constitution is read, and not the political leanings of the one reading it.
Below the official orange seal, the two most prominent methods of constitutional interpretation are defined, discussed, and another d-word that I can't muster right now. Keep in mind that this research is the result of a cursory Google and Wikipedia search, and is not exhaustive. I am not a law student, I am not an expert, and I will gladly defer to anyone with such expertise. This is merely what I have found.
Originalism is actually not a single theory and it should not be confused with textualism, though they are closely related. It is a term referring to two theories. Original intent, and original meaning.
Original intent is by and large not fashionable in modern legal proceedings, and should not be confused for what modern originalism actually is. Original intent refers to the concept that a court should only give a statute the power that its authors intended for its purpose. While this obviously creates problems for people who are not originalists, modern originalists have their own beef with original intent.
One of the major problems with original intent is assuming that Framers had a single, unified intent. It is highly unlikely that they had such intent on every part of the Constitution, and in the modern day the members of the House and Senate certainly do not share this united intent.
Original meaning is the more commonly adhered to school of thought for originalists, and the legal framework that modern Justices like Scalia and Thomas adhere to. It observes any questioned section of the Constitution and wonders aloud what a sensible person at the time that section was ratified might think it meant, and that what this sensible person believed must be held as the true extent of the law.
One unifying theory behind the concept of originalism is that the definition of the Constitution is unchanging. That the document means exactly the same things now that it does back when it was declared law of the land. This means that any new interpretations are not of any consequence during interpretation. In an originalist's point of view, if you want to change the meaning of the Constitution the document makes clear that an Amendment is your method to do so.
It must be stressed that while it is common for originalists to be conservatives, that the originalist interpretation cannot simply be labelled 'conservative'. An originalist would argue that it is not the court's place to determine what is and is not law, but that of Congress, and that the authority to determine what is and is not part of the Constitution is the authority of Article V - Amendments. Originalists can make judgements that piss off the conservatives- Justice Scalia's dissent in Hamdi v. Rumsfeld where he declared that Hamdi (an enemy combatant) must either be tried in normal court or that habeus corpus must be suspended is a noteworthy example.
Originalists firmly believe that the Constitution's meaning must remain unchanging save for Amendments, lest an 'activist' judge warp its meaning to the point where the Constitution means nothing at all. This is actually a legal view held by Thomas Jefferson, who while he certainly viewed the Constitution as flexible warned against excessive interpretation:
[t]he Constitution… is a mere thing of wax in the hands of the judiciary which they may twist and shape into any form they pleaseThe Living Constitution
There is no one word that can adequately describe the opposing viewpoint to originalism. The concept of loose constructionism has been around since the beginning of the country, but it was only in 1927 that Professor Howard McBain coined its modern name based on the title of his book.
The theory behind the 'Living Constitution' is that the Constitution's meaning is not fixed, but dynamic. Ideally, any interpretation of a constitutional case would not only take into account what the laws of the time at ratification were but also contemporary laws and viewpoints. Like originalism, this theory is not a single method of interpretations and can be broken into two points, though unlike originalism the two points are more complimentary than contrary.
The pragmatist approach attempts to point out that a Constitution whose definition is unchanging can result in unacceptable policies, and that therefore the meaning of the Constitution must change and evolve over time in order to remain a viable governing document.
The concept of original intent is still a viable one in this legal viewpoint, but from a different perspective than the originalists. While originalists believed that the Framers considered the Constitution a document whose broadness is it limiting factor, people who believe in loose constructionism believe this broadness to be a clear sign the Framers intended it to accommodate societal and technological changes.
For loose constructionists, this interpretation of broadness leads to the conclusion that the Framers were as smart as we gave them credit for and had quite a bit of foresight. This view is supported by the opinion of James Madison, the 'Father of the Constitution':
I entirely concur in the propriety of resorting to the sense in which the Constitution was accepted and ratified by the nation. In that sense alone it is the legitimate Constitution. And if that is not the guide in expounding it, there may be no security for a consistent and stable, more than for a faithful exercise of its powers. If the meaning of the text be sought in the changeable meaning of the words composing it, it is evident that the shape and attributes of the Government must partake of the changes to which the words and phrases of all living languages are constantly subject. What a metamorphosis would be produced in the code of law if all its ancient phraseology were to be taken in its modern sense.In modern times, loose constructionalism is viewed as the territory of 'activist judges' by conservatives. After all, who is to say that your interpretation is what the law actually says and not what you want it to say?
As a point of comparison, Canadian legal scholars strongly believe in loose constructionalism under the 'living tree doctrine' since their Constitution was explicitly intended to encompass unwritten legal principles. It has been a key facet of their legal system since 1929.
Both interpretations exist in the modern American legal system because the Constitution does not explicitly state how to interpret it. In the absence of such instruction, both originalists and loose constructionalists believe that their side is the one that was intended - with originalists pointing to the absence of instruction and constructionalists believing that the absence implies interpretation.
It is crucial to understand the competing interpretations of the Constitution in order to understand a great number of legal proceedings in the Court today. Here's a timely example concerning the Second Amendment. The text is as follows:
A well regulated militia being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringedWith the concept of state militias quickly becoming invalid in favor of a standing army, how do the courts view the Second Amendment?
-The originalist interpretation of the Second Amendment means that the Framers clearly intended for access to firearms to be protected, even if the idea of militias for state defense are no longer valid. Scalia himself has focused on the 'bear arms' part of the Amendment as a possible constitutional question for handheld missile launchers.
-A loose constructionalist would view the Second Amendment's right to bear arms as intended for the maintaining of state militias, which are obsolete. Some (but not all) would argue that if the Constitution had intended for private firearm ownership to be protected to this degree, that they would have specified it and not just on state militia service.
There are other cases in modern times where the two schools clash before us. Liberals and progressives often use the concepts behind a Living Constitution to justify the legality of gay marriage, government healthcare, and abortion. After all, how could the Founding Fathers have ever imagine the concept of such things, let alone the possible necessity of them?
Meanwhile, conservatives argue that if the government wants that authority.... well, draft a Constitutional amendment and try to convince everyone.
The constitutional schools of originalism and loose constructionism are tools with which we try to argue with. If you want a progressive future, if you want a future with gay marriage and the right to an abortion protected, and certainly if you want a government based on the Constitution who can be relevant to the changes of society, it makes sense to argue from a loose constructionist view. If you're in an argument with someone about such things, try it out.
1:01 PM PT: Update: Wow, this got rescued. I'm honestly flattered; thanks!