RECENTLY, OVER DINNER, I asked five friends what each thought the most powerful photographs of 2011 had been. The list of replies included journalistic photos from the Arab Spring to the Norway terrorist attacks to Occupy Wall Street.  Knowing I would pose this question and trying to anticipate my friends' responses, I had some of the images they referenced with me on my laptop. I pulled up the jpegs and then asked why they were powerful. The conversation that ensued moved between aesthetics and politics, with a few salient themes — the portrayal of vulnerability and its emotional impact on the viewer, a privileged access to something normally private, and the depiction of loss — recurring throughout.

Powerful photographs are generally not images of happiness — or only rarely, as in the case of a 2011 Getty Images photo of Phyllis Siegel and Connie Kopelov, the first same-sex couple married in New York City, which catches the two elderly women, one in a wheelchair, in a tender moment of affection. And even here the happiness is bittersweet: the celebration implicit in this photo is simultaneously a reminder of the long legal, political, and cultural battles that had to be fought to achieve this step forward, and of how little time this couple has left to enjoy their marriage. But still, that image represents a moment of triumph and love. Far more often, however, the most powerful photos, as they were discussed over this dinner, are images of suffering, loss, destruction, war, death, or disaster.

Why are these the powerful photographs? What about these images speaks to us? What, in fact, are they saying or conveying to us? I offer one case in point as an illustration of how our conversation progressed: A photograph by press photographer Justin Lane depicts a man in a suit kneeling before, and partially draped over, a commemorative wall at the North Pool of the new 9/11 Memorial in downtown Manhattan. It was taken on September 11^th of last year, at the memorial ceremony at Ground Zero. It's a quiet photo and a private moment, and those who have seen this image captioned will know that this man lost his son on September 11^th, 2001.

But what makes it powerful is not simply that it's an intimate image of loss and suffering, nor is it solely that it's beautifully composed — almost a black and white photo due to the lack of color in this scene, a strong beam of light running down the commemorative wall, and the focus sharply on the man while the background becomes soft and fuzzy. It is powerful for these reasons and also for two others, as my friends and I identified at dinner. The first, obviously, is that it refers to a defining moment in recent American history. The second is that, despite the specificity of the historical moment to which this image is pegged, it is also powerful in its openness. In tapping into a ten-year-long narrative, it allows any viewer an identificatory space in which to inscribe herself. How has 9/11 affected me? we ask.  Did I know someone who died? Where was I last year on the anniversary?  Moreover, even with a caption that tells us this man's name as well as his son's, we don't know these people. This man stands in fo...