The election could become bogged down in vote challenges and controversy
What will be the test of legitimacy for Afghanistan's elections?
No-one is using the age-old electoral mantra "free and fair".
It is hard to find anyone who expects Afghanistan's third major poll since 2001 to be fully free or fully fair.
These are the first elections since 2001 run primarily by Afghans - albeit with international support.
There has been an unprecedented level of political debate and lively campaigning in this first truly contested poll.
But one embittered election expert described it as a "squandered opportunity".
Some foreign election observers have worried for months what kind of language they will use the day after Afghans cast ballots on 20 August for a president and members of provincial councils.
The main issue for many people is security
Set the bar too high and disgruntled candidates will seize upon this verdict as convincing evidence that their victory was stolen. Set it too low and Afghans who've invested energy and hope in a crucial process, however imperfect, will feel badly cheated.
"Good enough" is a phrase that slipped into conversation after the last parliamentary elections in 2005, amid disappointment over some of the candidates allowed to run and persistent allegations of vote rigging.
In a highly charged political atmosphere, pressure was exerted on irate losers to accept the results and move on. Too much was at stake.
Western officials involved in the process now admit there was "very significant fraud". In some ballot boxes, neat piles of evenly folded ballots were evidence of stuffing.
A lot is also at stake this time, for Afghans and an international community determined to achieve success.
The question may be "good enough" for whom?
For all the talk of promoting democracy in Afghanistan, the ball was dropped after the 2005 polls.
Little was done to start work on this extraordinarily challenging process, despite a recommendation from the head of the Electoral Complaints Commission, Grant Kippen, to start preparations "well in advance of an election, including by means of a thorough lessons-learned analysis".
"We started too late," conceded a senior UN official.
In recent months, there has been a concerted push to fix gaping weaknesses and prevent the kind of fraud that could plunge Afghanistan into a political crisis at a critical juncture.
Some 17 million Afghans are eligible to vote on Thursday
Doubts persist about the preparedness and impartiality of the Independent Election Commission. But there is praise too for its efforts to try to meet a series of deadlines.
UN envoy Kai Eide called this exercise "the most complicated elections I have seen anywhere in the world".
Nothing can be taken for granted in a country still struggling to emerge from the heavy burdens of a quarter of a century of war.
How does a young election worker confront a powerful commander or tribal leader who arrives at a remote polling station with a stack of proxy votes from his village?
How do you hire and train thousands of women to carry out security searches in deeply conservative districts where women are rarely seen in public?
Afghan democracy may be a textbook all of its own. A myriad of influences and calculations weigh on voters in a political system driven by shifting networks of patronage and traditional loyalties.
But people who have survived a lifetime of hardship should not be underestimated. In earlier polls, despite Taliban threats and intimidation by armed commanders, Afghans still turned out in the furthest corners of the country boldly to exercise their right to vote.
The first presidential election after the fall of the Taliban was truly a high-water mark - an emotional, if not euphoric, moment in 2004 when more than 70% of Afghans turned out to give Hamid Karzai 55.4% of the vote.
Five years on, the past can seem like a different country. Many Afghans speak of deep disenchantment and disappointment. But as the polls approach, more people seem to have been drawn into the process, as presidential candidates campaign across the country and provincial council candidates raise issues that matter.
Nothing can be taken for granted in a country still recovering from war
Still, many Afghans cynically insist the result is "fixed" either in Washington or their own "wolaswali", their district.
But despite all the concern over electoral machinery, the biggest threat hanging over this election is security. In earlier polls, it is widely believed that Pakistan, then led by Gen Pervez Musharraf, played a key role in reining in the Taliban.
The Taliban have called a boycott this time, although it is still not clear how and where they will wield their threats.
Nader Nadery, who chairs the Free and Fair Election Foundation of Afghanistan (FEFA) spoke of his "mixed emotions".
FEFA will despatch some 7,600 Afghans, the largest observer mission, to polling stations across the country.
"There has been enthusiastic pre-election debate," Mr Nadery remarked. "But I'm still highly concerned about election day."
In Afghanistan in 2009, there is also talk of an "Iran" result - a repeat of the protests that erupted after its neighbour's deeply disputed presidential election in June. Some candidates and their agents have been warned by the Electoral Complaints Commission that this is dangerous talk.
But recrimination of some kind seems inevitable in a political system still seen as highly personalised.
Yet, for all the failings, many Afghans seem to agree the worst option is not to have an election at all.
"Do you believe there will be fraud?" I asked an Afghan businessman in Kabul. "Yes!" he declared emphatically, as if it was abundantly self-evident.
Do you think the elections should still be held? I replied. "Yes!" he declared with equal fervour.
"This election," he explained, "is just one more step in building our democracy. The elections next year will be better."
Afghans and foreigners are now vowing to start work on the 2010 parliamentary elections as soon as this round is over.
But if Election 09 fails the test of legitimacy, it could drag on for months, bogged down in vote challenges and controversy.
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