That's not (yet) what it means

Mark Bittman's piece on salt in the Times last week had a usage I'd never seen before. He wrote:

It does seem that as sodium intake in a population decreases, so does blood pressure, so public health officials argue -- not insensibly -- that most Americans (probably 90 percent!) would be smart to try to eat less salt.

Insensibly only makes sense here if you think it's the opposite of sensibly; Bittman (I think) means to say "not unreasonably." But that's not what insensibly has traditionally meant, to me or my dictionaries. 

The OED's (not updated) definition is "In an insensible manner or degree; imperceptibly; unconsciously; esp. so slightly or gradually that the action or process is not perceived; by imperceptible degrees."

And insensible here does not mean "contrary to common sense." The word did once mean "destitute of sense or intelligence; irrational" -- the OED's cites date from 1531 to 1794 -- but that sense is labeled obsolete. Merriam-Webster's online dictionary calls it archaic, as did the dictionary's 1913 edition; American Heritage (4th ed.) ignores even the possibility of that meaning.

But is archaic insensible poised for a 21st-century comeback? Well, Bittman isn't alone; examples of insensibly for "unreasonably, not sensibly" are out there, as early as 1986. Some sightings from the Times:

We ... took the measure of the 33-foot cross planted there, first erected by the Spanish conquistadors in the 1500s to counter the bad vibes from the volcano, which they regarded, not insensibly, as the gates of hell. (2007)

Sensibly, Mayor Rudolph W. Giuliani wants to get rid of the bad. But insensibly, cabbies say, the new regulations he proposes would not only run off the errant few but sideswipe several hundred of the good as well. (1998)

Sarge, a Hell's Angel from Lea Valley, England, was disappointed in his trip to Kruger Park, the crown jewel of the South African park system. Not insensibly perhaps, because he ... had arrived at an inopportune moment. (1996)

''The Indomitable Teddy Roosevelt'' is a curiosity: a documentary mixed in, but not insensibly so, with docudrama. (1986).

And from other edited sources:

...the group of iconoclastic individuals who insensibly condemned the arena to its fate to appease the Penguins. (Pittsburgh Post-Gazette, 2012, letter to the editor)

This is not the first time the Sense and Sensibility star has acted insensibly over the pursuing shutterbugs. (DigitalJournal.com, 2009)

In Colburn's case, appellate lawyers are arguing, not insensibly, that drugging the defendant into a torpor during his trial denied him his constitutional right to be competent. (Houston Chronicle, 2002)

Many observers believe, not insensibly, that developers of the tourist region around Niagara Falls would do better to form their own vision than simply to re-create what has already occurred. (Buffalo News, 2001)

Say "Y2K" with an anxious brow and all will know that one is worried, not insensibly, about the problem with computers. (Houston Chronicle, 1999)

Of course, for all I know this could be the dominant sense among the under-30 population. (There may be lots more examples out there for anyone willing to search "insensible" instead of "insensibly/not insensibly," but winnowing the results would take more time and patience than I have.) I wouldn't presume to resist the inevitable, but I would caution those who like this sense of insensible: The word can be hard to interpret even now, thanks to its many shades of meaning; it might be wise to resist adding another.