Left, the late Supreme Court Justice Antonin Scalia. (Kevin Lamarque/Reuters); right, Judge Neil Gorsuch (Chip Somodevilla/Getty Images)

Perhaps the biggest reason Republicans love Neil Gorsuch's selection as President Trump's Supreme Court nominee — apart from his age — is the fact that he's a demonstrated originalist.

Among conservatives, that's basically code for "not an activist judge." And among liberals, it's basically code for "conservative."

But the term is much more complicated than those admittedly over-simplified partisan views. So below, let's review what the term means and how it's evolved over the years.

What's the definition?

The Post's Supreme Court reporter, Robert Barnes, describes it thusly in Wednesday's newspaper:

Like [the man whose seat he'd assume, the late Justice Antonin] Scalia, Gorsuch is a proponent of originalism — meaning that judges should attempt to interpret the words of the Constitution as they were understood at the time they were written — and a textualist who considers only the words of the law being reviewed, not legislators’ intent or the consequences of the decision.

Critics say that those neutral considerations inevitably lead Gorsuch to conservative outcomes, a criticism that was also leveled at Scalia.

The Center for the Study of Constitutional Originalism at the University of San Diego School of Law defines it as "the view that the Constitution should be interpreted in accordance with its original meaning — that is, the meaning it had at the time of its enactment."

But I think University of Chicago law professor William Baude, an originalist scholar and former clerk for Supreme Court Chief Justice John Roberts, perhaps has the pithiest definition.

Baude defines it as "the view that law laid down by the framers in the Constitution remains binding until we legally change it, such as through the amendment process."

"Or differently," he said, "that the words in the Constitution have the same meaning over time, even if modern circumstances change, and even if we wish the words meant something else." (Emphasis added by me.)

What is its history?

The term is actually a relatively recently coined one, but its roots go back further.

In a 2011 paper, Georgetown University law professor Lawrence B. Solum writes that the first published instance of the term "originalism" in legal periodicals was in the early 1980s. The author, former Stanford law school dean Paul Brest, said he coined the term:

Brest used the terms “originalism” and “originalist” in order to refer to a position that he was criticizing. Brest’s term caught on, and eventually was adopted by proponents of the views that had affinities with the object of his critique. As a consequence, the words “originalism” and “originalist” are ambiguous – used by scholars, lawyers, judges, and the public in a variety of different ways. It seems likely that as a matter of lexicography, “originalism” is a family resemblance term – with several overlapping senses.

But Solum also noted that references to the "original meaning" of the Constitution appeared in the Yale Law Journal as far back as 1938. And in 1966, "original meaning" appeared in a Supreme Court dissent by Justice Hugo Black, who is now remembered as an originalist. In the years that followed, the original intentions of the founders would be a part of several opinions and dissents. Scalia first used the word "originalist" in a 1995 dissent.

Solum writes that, over the course of those decades, the theory behind those word choices changed. "The mainstream of originalist theory began with an emphasis on the original intentions of the framers but has gradually moved to the view that the 'original meaning' of the constitution is the 'original public meaning' of the text."

How do politics play into this?

People still disagree about precisely what it means — with the biggest chasm between supporters and opponents of originalism, as Solum notes. Appropriately, supporters believe in a narrower definition:

Legal theorists who self-identify as originalists are likely to strive to police the boundaries of the “originalism,” seeking to exclude implausible views and to focus debate on the versions of originalism that they believe are true, correct, or most reasonable. Legal theorists who oppose originalism may have precisely the opposite motivation, seeking to identify originalism with its least defensible variations. Political champions of originalism are likely to focus on simplified “sound bite” versions of the theory that conflate the content of originalist theory with the goals it seeks to achieve: “Originalism is the theory that judges should follow the law and not make it.” Likewise, political opponents might define originalism as a view that is obviously unpalatable: “Originalism is anti-woman.”

Essentially, supporters believe it's the purest form of legal interpretation and guard their definition fiercely, while opponents tie it to shameful episodes in our nation's past and discrimination. Scalia was on the receiving end of these accusations regularly, especially on issues such as race and gay rights. Even after his death, many attacked his decisions for these reasons.

Columbia University law professor Jamal Greene wrote extensively about originalism's "race problem" in 2011:

A racially sensitive constitutionalism must always, therefore, hold out the possibility of legitimate dissent from history. Originalism denies that possibility, and so for me, as I suspect for many African-Americans, it speaks in a foreign tongue.

In many ways, the debate over originalism mirrors the broader political debate over conservatism and progressivism — and brings with it many of the same connotations for each side. While conservatives believe they stand for the rule of law and smaller government, progressives believe them to be stuck in the past and holding up social change for certain classes of people. And while progressives believe they stand for compassion and government's role in society, conservatives believe them to be overly fond of throwing inefficient government spending at problems.

In Gorsuch, conservatives have someone whose legal philosophy lines up with their most basic political principles. Their overwhelming early praise is a reflection of that fact.