Ireland has Bloody Sundays and Bloody Fridays. Spain has Tragic Weeks, starting with an anarchist uprising in Barcelona in 1909. There have been bloodier weeks than the past seven days in Spain's recent history, but there can have been few moments when ordinary decent democrats felt such a sense of frustration and impotence, as ETA escalated its already ferocious summer offensive.
Six deaths (four self-inflicted), and more injuries, in four attacks in four cities in fewer days have led to comparisons with ETA's 1980 campaign, which claimed more than 90 lives. Such comparisons are still premature. But the group's capacity to strike at diverse targets right across Spanish territory has struck despair into many steady minds.
Again and again, Spanish governments have claimed that ETA is on its last legs. At least twice in the last decade, that was an arguable case.
In 1992 the key leaders of ETA were simultaneously arrested in France, and the organisation very nearly fell apart. Nevertheless, its political supporters became even more radical, launching the campaign of "street struggle" among teenagers which has provided ETA with a new recruiting pool.
In 1997 millions of Spaniards - and, more significantly, hundreds of thousands of Basques - took to the streets in furious protest at ETA's particularly coldblooded killing of Miguel Angel Blanco. (It seems to be a sign of weariness that, so far, the public response to ETA's equally ruthless current campaign has been much more muted.)
Despite the demonstrations, however, the following year ETA and its political wing succeeded in negotiating a remarkable agreement with the Basque Nationalist Party (PNV) and other moderate nationalists.
The Lizarra pact committed ETA to a ceasefire, as long as the moderate nationalists energetically pursued Basque self-determination by democratic means. This pact opened up a political and constitutional fissure in Spanish democracy which has grown wider and more dangerous with every passing month.
The PNV had been unique among democratic parties in Spain, in that it had not signed up to the 1978 constitution, because the party felt it did not recognise Basque sovereignty sufficiently.
It had, however, subsequently negotiated and operated extensive powers of autonomous government within the limits of that constitution. It had also actively rejected ETA's continuing terrorist campaign for full Basque independence.
Now, 18 years later, it was saying that both the Spanish constitution and the autonomy statute were "worn out".
It wanted to renegotiate something the major Madrid-based parties regarded as set in stone. These parties sometimes seemed as outraged by the prospect of "dismembering Spain" as they had been by ETA's violence.
In regional elections shortly after the ceasefire, ETA's political front got its best-ever results (close to 18 per cent), but the moderate nationalists stalled. The overall Basque nationalist vote was 55.5 per cent, its lowest share ever.
Both the major Madrid-based parties, especially the ruling centre-right Partido Popular (PP), increased their representation. The PP Prime Minister, Mr Jose Maria Aznar, saw an opportunity to displace the PNV as the biggest Basque party. This may have determined his subsequent hardline policy to the ceasefire.
While Basque nationalism has strong ethnic and linguistic roots, its ideology now sharply divides not only social groups but families. It is not unusual to find one family member supporting ETA, another the moderate nationalist PNV, and two more divided between the Madrid-based Socialists (PSOE) and the conservative PP.
These intimate schisms are reflected in the events of the last two years. ETA's ceasefire did not break down last December only because the Madrid government moved slowly on prisoner issues, and refused to engage in political negotiations with the terrorists. ETA reserved its bitterest contempt for the incapacity of the moderate nationalists to make progress on the sovereignty issue.
ETA's renewed campaign has left the moderate nationalists totally isolated. They have broken off institutional relations with its political wing, and repeatedly condemned ETA's new campaign. While the PNV is not directly in ETA's firing line, the businessman killed this week was a nationalist, and nationalist premises have been vandalised in "street struggle".
But the PNV refuses to abandon its political pursuit of Basque sovereignty, and seems to regard ETA as a sort of force of nature, which will erupt spontaneously as long as Basque sovereignty is not recognised.
Mr Aznar's government has consequently accused the PNV of being an "accomplice" of ETA's violence. While the Socialists, under the new leadership of Mr Jose Luis Zapatero, use more moderate language, they remain largely hostile to the PNV. As the terrorists push the political temperature towards boiling point, relationships between democrats have never been worse.
Twenty-two years after the restoration of democracy in Spain, ETA can no longer be dismissed as an unfortunate hangover from Franco's dictatorship. Nor can its members and supporters be regarded as children of May 1968 who never grew up. Many of them weren't born then.
The Red Brigades, the Baader-Meinhof group and the Angry Brigades have long since faded away, because they had hardly any popular support. Only the Irish and Basque conflicts maintained, as Churchill once put, "the integrity of their quarrel" into the 1990s.
The Madrid-based Spanish parties reject any analogy with Ireland, while Basque nationalists often exaggerate any parallels that do exist.
If one thing has been learnt in Northern Ireland, it is surely that protracted conflicts, where a significant sector of the population supports "armed struggle", can only be resolved by people who are prepared to think the unthinkable.
The Belfast Agreement showed that, in such situations, most citizens ultimately value peace - no more Bloody Sundays or Fridays - over the full implementation of the law.
The agreement has accommodated parties and points of view long regarded as taboo by mainstream democrats. It has granted political, and even ministerial, status to people who have supported the use of terror for political ends in a democracy.
Spanish democrats have made similar bold moves in the past, not least when they negotiated the transition to democracy with former Francoists. One has to wonder whether some form of Basque self-determination has to remain forever unthinkable for Spanish constitutionalists.
It is, of course, painful to even pose this question while ETA scatters human body parts across the streets. Sooner or later, however, someone in Madrid may have to ask it, if Tragic Weeks like the past one are not to keep recurring.
email address: woodworth@ireland.com