Brian Leiter is a professor at the University of Chicago Law School.

Ordinary Americans may be understandably perplexed by the controversy over nominating a judge to the highest court in the land. Isn’t appointing a top judge like appointing a top chemist? You want someone technically competent and professionally responsible, and that is all.

But all lawyers and all political insiders making the choices know that is not so. Appointing a judge to the Supreme Court is much more like appointing a head chef to a complex kitchen than appointing a skilled technician to apply scientific laws to determinate facts. The chef’s tastes and preferences matter, no matter his or her technical competence in the kitchen.

Consider what is obvious: There is no difference in terms of qualifications and expertise between President Barack Obama’s nominee to the Supreme Court, Judge Merrick Garland of the U.S. Court of Appeals for the D.C. Circuit, and President Trump’s nominee, Judge Neil Gorsuch of the U.S. Court of Appeals for the 10th Circuit. Garland graduated from Harvard Law School and clerked on the Supreme Court; Gorsuch also has a Harvard law degree and also clerked on the Supreme Court. They are clearly both very experienced and well-credentialed jurists. Yet Garland never even got an up-or-down vote in the Senate, while Republicans expect Gorsuch to be voted on and confirmed. Why all the high political drama?

The answer is simple and has to do with the fact that law is not anything like science — and that what the Supreme Court does has little to do with the dispassionate application of clear laws to clear facts.

(Peter Stevenson,Gillian Brockell/The Washington Post)

This should hardly be surprising. The court decides only about 80 cases each year and chooses those from 7,000 to 8,000 lower-court cases that parties want to appeal to the court. Unsurprisingly, cases are appealed where the law is unclear, where it seems the lower-court decision could have gone the other way. Parties also appeal cases when different circuits — the country is divided into 13 courts of appeals — have reached different decisions, which is most likely to happen when, again, the law is unclear. The Supreme Court chooses the most difficult among this vast array of lower-court cases to decide.

Given the complexity of the law and the complexity involved in saying what really happened in a given dispute, all judges, and especially those on the Supreme Court, often have to exercise a quasi-legislative power: They have to decide what should be done based on their own moral and political values, since existing legal standards conflict, or are indeterminate, or are silent on the problems they confront. The Supreme Court, as the final court of appeal in our system, is the super-legislature of last resort. And that is why Republicans blocked Garland’s nomination and why Trump chose Gorsuch. Republicans expected Garland to vote against their objectives on the super-legislature. Trump expects Gorsuch to vote with the Republicans.

None of this is controversial among insiders. Judge Richard Posner of the U.S. Court of Appeals for the 7th Circuit — nominated by President Ronald Reagan — made these points less than a decade ago in his book “How Judges Think,” while Benjamin Cardozo — nominated to the Supreme Court by President Herbert Hoover — delivered the same lessons in “The Nature of the Judicial Process” nearly a century ago. All jurists know that good judging demands not simply technocratic expertise but moral and political judgment of the kind exercised by a conscientious legislator.

Supreme Court nominations are controversial because the court is a super-legislature, and because its moral and political judgments are controversial. As a super-legislature, it has limited jurisdiction, depending on what cases are brought before it, but those cases are important enough. Just as no one would expect Republicans or Democrats to assent to appointments to the Senate without regard to political ideology, it is naive to expect anything similar in the case of nominations to the Supreme Court.

And that is why Senate Majority Leader Mitch McConnell (R-Ky.) would not let Garland be voted on last year and why Trump nominated Gorsuch. Perhaps it is time to tell the truth to the public so that we might have honest hearings about the moral and political views of the nominees.