Diplomats from Iran and the 5+1 Powers have gathered in Vienna, likely to last more than two weeks, to reach a comprehensive settlement over Tehran’s nuclear program. Yet paradoxically, given the intensity of an effort, the possibility of a deal may be receding.

Here are five points — and one word (“centrifuges”) — why the future may offer conflict rather than hope.

1. BOTH SIDES WANT A DEAL

Forget any noises from hardliners on the sidelines in Washington and Tehran about the dishonesty and perfidy of the “enemy”. The US, its partners in the 5+1 Powers, and Iran all want a deal before the expiry of the Joint Plan of Agreement on July 20.

That is because the stakes are high in an unstable failure. Washington would face the escalating tension of animosity as the Middle East lurches from crisis to crisis, not to mention pressure from Israel and its supporters — including some in the US — for a military strike on Iran. Europeans would be locked into the dispute that is affecting their possibilities for trade, as well as hindering diplomacy. Russia and China would be caught between the desire to ally with Iran on a range of issues, as well as expanding economic links, and the requirement of a united 5+1 line.

And the Iranians would be confronted with an ongoing economic crisis with little sign of relief.

Iran and the 5+1 Power took notable steps towards resolution in November’s interim agreement. As the US and European partners implicitly recognized Tehran’s right to enrichment for the first time, the Iranians suspended the production of 20%-enriched uranium, diluting existing stock to 5% or converting it to oxide power for fuel plates which cannot be used in a military program.

2. BUT CENTRIFUGES ARE THE MAIN OBSTACLE

Centrifuges are used to enrich uranium to a state where it can be used for civilian or military purposes, from medical isotopes to reactor fuel to an atomic bomb.

The number of those centrifuges, and the state of their development, is the primary issue in the way of a comprehensive settlement.

While Iran has given up 20% uranium, it wishes to produced 5%-enriched uranium with tens of thousands of centrifuges. Currently, it has 19,000, with about 10,000 operational; however, it has publicly expressed desire for 50,000 — and many mores — in recent weeks.

The US and European allies say that Iran does not actually need 5% uranium, as its nuclear reactors are being supplied by Russia under a contract to 2021. However, if Iran insists on domestic production, the Americans and Europeans want the number and level of centrifuges sharply curtailed — probably to no more than “several thousand”.

The US-Europe case is that the 19,000 existing centrifuges, let alone an expanded stock, can be set up in assemblies which can quickly move uranium from 5% to 20% and then to the 90%+ required for a nuclear weapon. They argue that this is a “break-out” capability which cannot be tolerated.

The Iranian respond that they must have self-sufficiency in uranium production, as outside suppliers — include Russia — have reneged on commitments in the past. Besides, Tehran argues, this is the right of a sovereign nation. Unlike other nations which have escaped scrutiny and obtained the Bomb — Israel, Pakistan, and India are all examples — the Islamic Republic says it is being singled out for punishing treatment.

The US and Europe say that Iran is not like “other nations” because it hid its nuclear program until 2003. Even if Tehran is now saying that it will work with the International Atomic Energy Agency to prove its compliance, the US-Europe line is that Iran could block IAEA inspections at any point as it pursued “break-out”. Even if break-out time was months, rather than weeks, the Islamic Republic could have military nuclear capability before an international coalition could be mobilized to stop it.

All of these positions can be debated, but both sides are genuine in their commitment to the positions. Western officials — some of whom are violating the insistence on secrecy in the talks and spinning to the media in Vienna — are making clear that Iran will not be allowed to hold their 19,000 centrifuges, let alone expand the stock.

And there is an additional complication which has escaped public notice so far. Iran is insisting that it will introduce the IR-2m model among its centrifuges, having developed its capability at the start of 2013 while refraining from installation.

The Western powers are firm that Iran must stick with its 40-year-old IR-1 centrifuges. Any replacement, they maintain, must be “like for like”, procluding introduction of the IR-2m and development of even more advanced models.

3. WILL THERE BE AN IRANIAN CONCESSION?

The US line, shared by at least some of its European partners, is that Iran will eventually give way because it fears the alternative of no deal.

Put negatively, Tehran will face even more economic hardship, as sanctions continue to tighten and the Rouhani Government grapples with years of mismanagement, corruption, and distortions in both the public and private sectors. Put positively, Iran can expect a surge in trade and investment — albeit not immediately, given the web of sanctions to be lifted — if a settlement is reached.

It is true that the Supreme Leader was convinced last autumn by President Rouhani to resume nuclear negotiations because of the grave prospects for the Iranian economy. It is also true that the economic tension played a part in Iran’s acceptance of the Joint Plan of Agreement, which was more favorable to the Western powers than to Tehran, and to tolerate delays in measures such as the unfreezing of Iranian assets.

That is far different, however, from Ayatollah Khamenei’s approval of a comprehensive deal which would include a sharp reduction in Iran’s domestic capacity for uranium production. Put bluntly, this is a domestic political as well as economic issue, and pride in sovereignty matters as much as fear of the pressure on Iranian exports and production.

That is especially true for President Rouhani and his inner circle. Their political survival rests upon a return to Tehran with a deal that can be presented as a “win” after years of US and European challenges. That “win” of recognition of an Iranian civil nuclear program will be hollow if it rests upon years of shackles on enrichment.

The Western case is that Rouhani can present the Supreme Leader and the Iranian public with the windfall of sanctions relief. But that is asking those audiences to accept immediate political sacrifices for the prospect — but not the assurance — of benefit sometime down the road.

Even if Rouhani wanted to make that gamble, he would be handing his fate to hardliners who have warned that the President and his negotiators would be weak when put to the test. That allegation has been curbed since January by the Supreme Leader’s insistence that the process of talks must be played out to a conclusion, but it will revive if the deal looks like an Iranian capitulation.

4. SO WHAT CAN BE DONE?

Plan A would be a settlement which preserved the appearance of both sides getting reassurance. For example, an arrangement which accepted Iran’s 19,000 centrifuges, while spelling out the allowances for both the introduction of the IR-2m and the number of centrifuges in operation, could meet both Iran’s need to show an “independent” domestic program and the US-Europe requirement of no break-out capacity.

But so far, the Iranians are not even countenancing the status quo — if anything, they have raised the number that they are putting on the table — and the US-Europe line is unyielding that only several thousand centrifuges can be in play. Alternative proposals such as measurement in work units or the placement of some centrifuges — assembled or awaiting assembly — “in escrow” outside Iran, until their use can be approved by the International Atomic Energy Agency, do not appear to be on the table.

The US-European hope does not appear to lie in a creative resolution of the core issue, giving Iran some notion of self-sufficiency while meeting concerns over “break-out”. Instead, they appear to believe that Iran will see the light — or, put another way, avoid the further punishment of sanctions — by conceding a reduction on the centrifuges.

And if that does not happen?

Plan B would be an acceptance that the July 20 deadline cannot be met, extending the interim Joint Plan of Agreement to allow for more discussions.

However, even if that extension was agreed, it offers no way to resolve the centrifuge dispute — a month, three months, or six months from now. Meanwhile, the US Administration would be under pressure from Congress to stay away from the discussions, and the Rouhani Government would be under pressure from its opponents to concede failure.

That would leave a far-from-promising Plan C. The US and partners, notably France and Britain, would return to the well-worn strategy of economic pressure. The Supreme Leader would not only proclaim the “resistance economy” to rally Iranians against the “enemy”; he would seek to implement it, presenting the resulting sacrifice as a valiant defense to match Iran’s eight-year war with Iraq in the 1980s.

5. TALKING PAST EACH OTHER INTO A FUTURE OF CONFLICT

The hope fostered by November’s interim agreement was that each side would recognize the key concerns of the other, while trying to defend their interests.

That appears to be eroding despite the “good atmosphere” of the discussions. The Iranians do not appear to accept that “break-out” is not just a strategem, fostered by neoconservatives and the Israel lobby, to force their capitulation; it is a genuine concern not only of the US but of the other 5+1 Powers. The Americans and European partners do not appear to recognize that Iran cannot sign an agreement which enshrines its permanent dependence on others for uranium supply — for ideological, political, economic, and technological reasons.

Even more worrying, neither side appears to have planned for the consequences of failure. With expectations raised with the breakthroughs of the last year, the fall will be even greater if there is no settlement. The US Administration will be back in the cul-de-sac of perpetual sanctions. The Rouhani Government will be weakened to the point of impotence, as hardliners grab the political high ground in Tehran.

No one is talking about those gloomy prospects, since these would dispel the public line of all efforts for an agreement by July 20.

That might be smart politics, but it also might be wilful evasion: unless both sides come off their fixed views on centrifuges, disillusionment, suspicion, and hostility will be added to the mix of crises — including Iraq and Syria — that are already promising a less-than-stable future for both Washington and Tehran.