Shouldn't plain language be the criteria? Only a mind reader who can communicate with the dead can know original intent.
Wait, how can a mind reader read the minds of the dead?
"Shouldn't plain language be the criteria? Only a mind reader who can communicate with the dead can know original intent."
Not quite. The Founders wrote lots of material about why they wrote the Constitution as they did. The fact that it's difficult does not mean we might as well not try. Remember, liberals' notion of "plain language" is, well, whatever they wish the language said. That's just how they think. But with history, we can more readily refute liberals' interpretations.
Take, for example, the second amendment. Liberals take the phrase "well regulated" as a plain indication that the federal government can restrict our use of guns. They don't quite ignore the "shall not be infringed" part; they just say it means that guns can't be banned altogether, but they can be thoroughly regulated.
Without knowing history, I'm not sure their argument would necessarily be wrong. But in fact, the language of the second amendment came right out of state constitutions, and at the time, all of those states interpreted the clause as meaning the federal government can't touch our guns, because the states need to have effective militias.
Today, "well regulated" means something very different than it did 200 years ago. That's why history matters.
Another point to consider is that the meaning of words change over time. For example, it matters greatly that the definitions of the terms for militia and regulated have taken on different contexts today than they had in the 18th century at the time of the ratification of the Constitution. When we think of a militia, we tend to think of a group like the National Guard. The National Guard IS a militia.....but it is not THE militia. The militia in the 18th century was any able bodied male capable of carrying and using a firearm. A "select" militia was one that receives pay, training, and tasks above and beyond what is expected of the general population. When we think of "regulated" today, we think of controlling by means of laws - ergo gun control. However, the Oxford English Dictionary, 2nd Edition, (1989) defines regulated in 1690 to have meant "properly disciplined" when describing soldiers:
[obsolete sense]
b. Of troops: Properly disciplined. Obs. rare-1.
1690 Lond. Gaz. No. 2568/3 We hear likewise that the French are in a great Allarm in Dauphine and Bresse, not having at present 1500 Men of regulated Troops on that side.
An originalist would therefore strive to determine what was intended by the document, using the plain language of the document, as well as other writings and even other actions of the government at the time to discern what the reasonable and original interpretation of the law was and then to apply it to the present day situation. For an example, read Justics Scalia's dissent in the Kentucky 10 Commandments case. He exhaustively goes into the history of the interaction of government and religion at the time that the Bill of Rights was passed to discern whether or not the Founders and the people who ratified the Constitution really intended to "erect a wall of separation between Church and State" which they clearly did NOT intend to do.