The issue has surfaced persistently in recent decades. But there are now new nationalist urges across Asia, with a rising China and geopolitical tensions in the South China Sea. Japan has been grappling with its post-war national identity for years, and the present government is determined to revise its pacifist Constitution.

By definition, a nation-state has to be nationalist in one way or another - especially when its leaders perceive it to be vulnerable to internal and external threats. Nationalist sentiments are shored up by portraying an uncertain present and projecting a vision of a more secure future. This also entails specific ways of remembering or forgetting the past. In the Japanese case, this is illustrated by the repeated visits of prime ministers to the Yasukuni Shrine, which honours the country's war dead, and by their avoidance of an unqualified apology for wartime atrocities.

The celebrations in Singapore will culminate on Aug 9, our National Day. But I am reminded that the same date 70 years ago has another kind of significance in global history: the dropping of the second atomic bomb on Nagasaki, three days after the US Air Force dropped the first bomb in Hiroshima.

"Under a summer sky," as Paul Ham put it, "without warning, hundreds of thousands of civilian men, women and children felt the sun fall on their heads." Those fateful seconds - the blinding light, the swelling fireball, the rising mushroom cloud - marked the dawn of the nuclear age, a new age of perpetual insecurity as more countries, big and small, entered the global arms race.

To this day, historians have asked whether the bombs should have been dropped at all, and dropped on civilian populations, and whether Nagasaki could have been spared after Hiroshima. The scholarly consensus - although still debated - is that the political decision to use the bomb was made in spite of the military assessment that Japan's surrender was imminent.

One insightful analysis is provided by the American historian of modern Japan, John Dower, who wrote about the 50th anniversary of the end of the war in 1995. He highlighted the "three narratives of our humanity" that emerged in the memory of the bombings.

The first narrative, "Hiroshima as victimisation", describes the recollection of war sufferings among many Japanese, especially the trauma of the bombings. Dower, however, noted that the "victim consciousness" also fostered pacifist and anti-militaristic sentiments and was combined with a "victimiser consciousness", a growing acknowledgement of Japanese war crimes.

Here, we may recall what Kuo Pao Kun, our mutual friend, said at a meeting of Asian intellectuals in Singapore. This was in 2000, two years after he wrote The Spirits Play and two years before he died at the age of 62. His play about war and memory was inspired by his visits to the Japanese Cemetery in Singapore and it was completed after spending months in Japan. Pao Kun said: "I think that of all peoples the Japanese have in their living memory the most profound understanding of the war because the Japanese were at the same time a very cruel aggressor and a victim of the cruellest experience of war."

The second narrative, "Hiroshima as triumph", was embraced by many Americans. The bombings symbolised the decisive heroic act that ended the war. This purportedly saved a great number of American lives from further Japanese aggression, which had begun with the "infamy" of the Pearl Harbour attack in December 1941. There is no room for moral ambiguity here, including any idea of the Japanese as both victimisers and victims - a view which does not necessarily imply any moral equivalence between the violence inflicted by the Japanese throughout the war and on the Japanese and other nationalities (including Koreans and Japanese-Americans) in Hiroshima and Nagasaki.

This leads to the third narrative: "Hiroshima as tragedy". As Dower wrote, "We confront not just an American or Japanese tragedy but a tragedy of our modern times". The atomic bomb was a product of advanced technology, a single weapon capable of instantaneously exterminating human targets invisible from the skies. By that time, however, the taboo against killing masses of non-combatants was already broken. Japan, Germany, Great Britain, and the United States had begun the indiscriminate firebombing or "terror bombing" of cities. The decision to use the atomic bomb was not regarded by the Americans and their Allies "as posing any particularly acute moral dilemma…(and) was arrived at without great soul-searching and certainly without significant internal debate".

The tragedy of the war does not lie only in the unprecedented human destruction that followed from the Japanese decision to wage war and the American decision to use the bomb. It lies in the fact that these inhuman decisions were made by small groups of men - and they were all men - without the exercise of deeper human judgment.

This tragedy also casts a darkness over entire populations. Although citizens were not party to the decision-making, most either actively supported or passively went along with the decisions. Yet, we also wonder how many felt powerless and speechless in the face of larger, impersonal forces. Perhaps we must contain our self-righteous moralism today by asking: If we were in their shoes, should we, could we, would we have acted differently? And if not, why not?

Pao Kun asked our Japanese friends: "What is there in the Japanese psyche, what is there in the Japanese culture, that stops a people capable of deep, profound thinking coming out strongly as a people, not just a few individuals but as a people, to reflect openly and deeply about the war? Because, what you have in you is an insight into the war that none of us have in such depth."

Indeed, a similar question might be asked of intellectuals in any country as they confront the traumatic and tragic events of their nation's past. For, every narrative of the past is a narrative of a particular humanity.

I know you share the hope that the passage of 70 years presents us with new opportunities for more open and deeper reflection. As post-war baby boomers, we have had the privilege of becoming friends and living through a new era in Asia. Those who directly experienced - and survived - the war are now either dead or in their late years.

The question is whether a living memory dies with them.

We are members of an in-between generation, who can bridge the gulf between the dead or dying generations and the young, for whom the past has either faded from memory or is incompletely recounted in textbooks and the media.

This is why I value the honest conversations that we have all tried to facilitate among independent Asian intellectuals all these years. This is why I did not want this sixth day of August to pass without writing to you.

And now I return to face my students, as we all face what it means to live in a morally complex world.

As ever,

Kian-Woon

• The writer is a sociologist who teaches at Nanyang Technological University.