My great-grandfather Timothy Lee was the first policeman of Irish ancestry on the Lynn, Mass., police force. He overcame prejudice to get there -- the kind that posted "No Irish need apply" signs in the windows of Boston businesses. Great-grandfather Tim was able to hurdle the barriers of prejudice by enlisting in the Union Army at 15 (he lied about his age) and returning home as a veteran. In the city of Lynn, he benefited from the newly enacted veterans' preference in government jobs that took down the "No Irish" sign.

From family accounts, Tim was a tough cop. I have in my possession his well-used leather blackjack to show that he might have smacked a few dozen heads in his time.

Flashing forward to the city of Cambridge, Mass., in July 2009, another policeman of Irish ancestry, Sgt. James Crowley, made national news for his arrest of renowned black scholar Henry Louis Gates Jr., on the porch of Mr. Gates' Harvard University-owned home following a report of a break-in by two black men. Mr. Gates and his supporters responded by charging Sgt. Crowley with racial profiling -- long-hand for racism -- since Mr. Gates had identified himself as the owner of the home. Sgt. Crowley's response was that he remained concerned about whether there was a second black man on the premises. Regardless, he arrested Mr. Gates for disorderly conduct rather than in connection with a burglary.

Not helping the situation, the far-sighted President Barack Obama weighed in from 440 miles away in Washington, D.C., to pronounce that the Cambridge police "acted stupidly" in arresting Mr. Gates, who is Mr. Obama's friend. Granting that he did not know all the facts, Mr. Obama did not hesitate to express a harsh judgment of the events that ensued in Cambridge.

I would suggest that what we have here is not only a failure to communicate, but an encounter between a nationality and a race both with a history of oppression.

Little more than 150 years ago, many Irish-American men were hod carriers confined to living in ghettos such as the Brickyard in Lynn. In the same time frame, the majority of African-American men were slaves to white masters. Today we live in a country that is dotted with black ghettos in many major cities as well as less visible (because of skin color) Irish ghettos.

Is it any wonder that an encounter between a policeman from one of these backgrounds and an academic from another might be loaded with the baggage of past oppressions?

Also in play in the Gates-Crowley confrontation are centuries of town-gown tensions between the citizens of working-class Cambridge and the privileged population (at least in its own perception) of the students and faculty of Harvard University.

Mr. Gates is perhaps Harvard's most famous professor. Sgt. Crowley is a conscientious cop. Inside and on the porch of Mr. Gates' residence, the professor was unwilling to concede an inch to the agent of law enforcement, and law enforcement was unwilling to grant special privileges to the academic. The standoff became belligerent, and Mr. Gates' vociferousness resulted in his arrest.

I agree with the supporters of Mr. Gates that it is the responsibility of a police officer to defuse a situation once a determination of innocence has been made. In this case, Sgt. Crowley was able to determine that Mr. Gates was in his own home. Yet Sgt. Crowley's refusal to back away from the situation -- quite a different thing from backing down -- triggered a response from Mr. Gates that is understandable in light of the history between black males and white policeman.

This may be the right time for a history lesson that looks back at the oppression shared by Irish- and African-Americans. My great-grandfather Tim Lee's generation made no secret of its prejudice against blacks, yet the passage of time and arrival of new generations has changed that perspective. The United States may not be post-racial, but in general it is more open-minded and accepting.

I suggest a mutual apology is in order. Sgt. Crowley's confident assertiveness touched off something deep in the consciousness of Mr. Gates. The professor's equally assertive insistence on his rights challenged the authority of Sgt. Crowley in a manner that Sgt. Crowley could not rise above. Given his friendship with Mr. Gates, Mr. Obama should have declined to comment rather than add fuel to the fire.

To recover from his impolitic use of the word "stupidly," Mr. Obama now plans to bring the men together at the White House for a beer. There he can apologize to both of them for having aggravated the situation.