This week the US Supreme Court heard oral arguments in the most controversial case of the year, the long-awaited challenge to Roe v. Wade and abortion rights.

In Dobbs vs. Jackson Women’s Health, the state of Mississippi argues that a 2018 state law banning abortions after the first 15 weeks of pregnancy is constitutional.

The to-and-fro between the lead lawyers for each side and the justices of the Court revolved around two issues: the viability standard and whether the Court’s hands are tied by precedent.

The Mississippi statute, which was passed in 2018 but was immediately appealed, sets a limit of 15 weeks of pregnancy for abortion. But Roe v. Wade sets the limit at “viability”, an ill-defined and constantly changing standard. The other precedent is Planned Parenthood v. Casey, a 1992 decision that reaffirmed the “central holding” of Roe v Wade that “viability marks the earliest point at which the State’s interest in fetal life is constitutionally adequate to justify a legislative ban on nontherapeutic abortions.”

From her questioning it seems that Justice Sonia Sotomayor was inclined to let the standard of viability stand. The counsel for Mississippi, however, responded that “the fundamental problem with viability, it’s not really something that rests on science so much. It’s that viability is not tethered to anything in the Constitution, in history, or tradition. It’s a quintessentially legislative line.”

The line of questioning was not favourable for the pro-choice side.

The counsel for the abortion clinic identified liberty (or choice) for women as the central issue of the case. But the Chief Justice, John Roberts, queried that: “if you think that the issue is one of choice, that women should have a choice to terminate their pregnancy, that supposes that there is a point at which they’ve had the fair choice, opportunity to choose, and why would 15 weeks be an inappropriate line? viability doesn’t have anything to do with choice.  But, if it really is an issue about choice, why is 15 weeks not enough time?”

It may be difficult for non-lawyers to appreciate this, but the biggest obstacle to striking down the 1973 decision in Roe v Wade is precedent: simply the fact that it happened. In principle the Court respects the decisions made by previous courts – and in this instance, it has even reaffirmed it in another major case, Planned Parenthood v. Casey, in 1992.

This is the legal doctrine called stare decisis, or “let the decision stand”. Justice Amy Coney Barrett described it this week as “obviously the core of this case”.

In the oral arguments Justice Sotomayor even suggested that the right to abortion was so deeply entrenched in American society that overturning Roe v Wade would threaten the authority of the Court. “Will this institution survive the stench that this creates in the public perception that the Constitution and its reading are just political acts?”

Many pro-choice advocates agree with her that the doctrine of stare decisis means that Roe v. Wade must not be overturned. Some politicians have argued that Roe v. Wade is a “super-precedent”, a case that has become established as part of the national ethos.

The Supreme Court will probably not hand down a decision for several months.