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The columnist Russ Douthat wrote recently in The New York Times that “Trumpism is also a creature of the late Obama era, irrupting after eight years when a charismatic liberal president has dominated the cultural landscape.”

It’s too easy to suggest that perhaps Douthat meant “erupting/eruption,” near-homophones of “irrupting/irruption.” After all, what he was suggesting was that Trump and his politics had a “bursting forth or out,” or “a sudden outburst, as of emotion or social discontent,” as Webster’s New World College Dictionary defines “eruption.”

But two days before Douthat’s most recent piece, The Tallahassee Democrat wrote about a flock of cedar waxwings descending on local gardens: “There is a special word that describes the sudden arrival of large numbers of the same species of bird, like flocks of cedar waxwings. This word is ‘irruption’—ir, not er.”

The article continued:

Sometimes irruptions involve a species that is relatively common to an area, but mostly they involve unexpected birds that are seldom seen in the local vicinity. According to the website About.com, an irruption is defined as “a dramatic, irregular migration of large numbers of birds to an area where they aren’t typically found, possibly at great distances from their normal ranges.”

In some ways, then, Douthat’s selection of “irruption” is quite wry. Trump is an outlier, used to places like New York and Palm Springs, who finds himself in Iowa, Nevada, New Hampshire, South Carolina, etc., places where he’s not typically found. Not to mention that he is running as a conservative despite a more liberal background.

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It wasn’t the first time that Douthat has used “irruption” in reference to Trump. In September, he wrote, “I’ve written a number of pieces and posts on how the Donald Trump phenomenon could represent the irruption of something genuinely interesting into Republican politics … .”

And Douthat isn’t the only one to apply that unusual phrasing to Trump. Earlier in February, a Vermont columnist wrote of the Republican Party: “But suddenly, with the populist irruption of Trump and Cruz, neither of whom expresses any interest in party orthodoxy or support, the conservatives seem in tatters.” Here, Trump and Cruz are the unfamiliar species within the GOP.

Even so, of the nearly 90 Nexis hits of “irrupt” or “irruptions” in news reports from the past six months, all but a handful refer to species, specifically birds that suddenly flock someplace unusual in large numbers.

One other “irruption” also appeared in The Times recently, in a music review of all places: “ ‘Streaming Arhythmia’ ends with a final series of irruptions—swift releases of musical tension.”

That “swift release” sounds a lot more like an “eruption” then anything else. Indeed, WNW defines the verb “irrupt” as “to burst suddenly or violently (into)” as well as its scientific meaning, “to increase abruptly in size of population.”

That “(into),” though, is key in understanding the difference between “eruption” and “irruption.” In a volcanic “eruption,” lava, ash, and other things burst forth, or out.

But in an “irruption,” the explosion occurs the other way, into something. Also think about the prefix in each case: An “e” indicates “external,” while an “i” indicates “internal.” An “eruption” goes out, while an “irruption” goes in.

So perhaps Douthat was being even more subtle, using “irruption” in the invading sense, not the flocking sense, but wanting the evocation of an exploding “eruption” as well.

After all, both can be violent, both can be sudden, and, just as volcanologists have difficulty predicting an “eruption,” politics wonks can’t predict an “irruption,” either.

Especially when it comes to a species as unpredictable as Donald Trump.

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Merrill Perlman managed copy desks across the newsroom at the New York Times, where she worked for twenty-five years. Follow her on Twitter at @meperl.