"Gilead then cut Ephraim off from the fords of the Jordan, and whenever Ephraimite fugitives said 'Let me cross', the men of Gilead would ask, 'Are you an Ephraimite?' If he said, 'No', they then said, 'Very well, say Shibboleth.' If anyone said Sibboleth, because he could not pronounce [the sh sound], then they would seize him and kill him by the fords of the Jordan."

Since the authors of the Old Testament put that tale of watchwords and brutal border security into the Book of Judges, the very word shibboleth has come to represent a form of words or ideas that sets insiders and outsiders apart. This isn't always a bad thing. If you're standing guard at night, far from the village fire, and the twigs snapping underfoot out there in the inky void are getting closer and closer, they might be here to steal your cattle or kill your family. It's important to tell friend from foe.

In modern usage, a shibboleth is a truism which, bundling together a dense packet of emotions and historical arguments like DNA in a gene, is so patently true that it requires explanation only to cultural outsiders.

And the surest way for an outsider to offend is to force insiders to defend or even explain the reasoning behind a shibboleth. To be forced to do so, in one's own country, is on some level as threatening as the night sounds to the primeval sentry.

Nuclear technology is evil and Ireland will have nothing to do with it. Here's one shibboleth that's getting tested lately. Threats to energy security and from climate change are suddenly making that truism look less like prudence and more like moral conceit. At the moment, the 'nuclear is evil' shibboleth is still sufficiently powerful that the most anyone will predict is that the ESB (or its daughter companies once it's broken up) will buy nucleargenerated electricity across a European grid. (The fact that we already buy nucleargenerated electricity is immaterial. The question is whether we can admit it. ) Israelis are brutal bullies who oppress Arabs. That's another contemporary shibboleth, if laden with irony.

The current conflict began when an Israeli patrol was caught off guard by Hizballah guerillas inside Israel, with several Israeli soldiers killed and two kidnapped. How the Hizballah snatch squad managed to cross one of the earth's more vigilant frontiers is a bit of a mystery, and a tactical triumph, but clearly someone didn't stop them and ask them to pronounce the watchword.

Israel's response is disproportionate. Intentionally so.

Invading Israeli territory and bombing Haifa with rockets are acts of war, carried out by a state or not, and Israel will hit those responsible and anyone who harbours them. Future raids will be deterred by making the cost horrifically high.

My only problem with what Israel has done is that they're hitting the wrong country. I'd prefer if they produced a chain of evidence leading to Syrian intelligence and bombed those buildings in Damascus, if only because Robert Fisk doesn't live there.

But to say even that and thus reveal that my first sympathies are with the Israelis is to mark myself as an outsider, who for the last six years found horrifying what I perceived to be the lack of balance in the Irish media when Israel is discussed.

Then again, I grew up with a different set of shibboleths.

Shibboleths are not forever. Attitudes and beliefs change, even at the ideological DNA level.

The process by which they change is complex, but the fact that, in the last few decades, Thomas Kuhn's "paradigm shift" and Malcolm Gladwell's "tipping point" have become the sort of phrases columnists drop in their articles to make themselves seem well-read, at least tells you that the very pace of that change has accelerated.

Even in Ireland. One shibboleth . . . Ireland as Cead Mile Failte . . . will, I predict, be gone entirely by the end of this decade, when attitudes turn against immigrants and opposition to immigration becomes an explicit appeal of a Fein-ish political party.

Which will make the other shibboleths, marking insider from outsider, all the more potent.