Mr. Romney’s manner of speaking is essentially the verbal equivalent of his public persona: flat, one-dimensional, unable to connect. It is striking that he sounds almost the same in every speech, regardless of the audience. Observers have chronicled the wooden, monotonous nature of his delivery, the lack of tonal variation, the multiple hedges, the forced laughter, the “Leave It to Beaver”-era “gosh”-ness of his speaking. A painfully awkward example: his attempt to interact with black youngsters, at a parade in Jacksonville, Fla., for Martin Luther King’s Birthday in 2008, where he dully barked: “Who let the dogs out? Woof, woof.” During the primary campaign this year, he was mocked as inauthentic for throwing in some “y’alls” while stumping in the South.

This linguistic judgment is not based on race or party. Our last three presidents have all been able to shift their speaking styles — an ability that is distinct from eloquence or empathy. Both Bill Clinton and George W. Bush were known for speaking in a “folksy” manner: Mr. Clinton with black and Southern audiences, and Mr. Bush with Southern and Latino audiences (he would even switch into Spanish in his speeches). Before them, Lyndon B. Johnson was perhaps the president most notable for variation in speaking style. More recently, the blunt (and occasionally profane) style of Gov. Chris Christie of New Jersey, and the strategic sprinklings of Spanish by Gov. Susana Martinez of New Mexico and Senator Marco Rubio of Florida, have contributed to their rising profiles in the Republican Party.

In 2008, Mr. Obama took the linguistic flexibility of his predecessors to new heights. Take, for example, his style-shifting during a visit to Ben’s Chili Bowl, a well-known Washington eatery, days before his inauguration in 2009. In a scene captured on YouTube, Mr. Obama declined to accept the change from a black cashier with the statement “Nah, we straight.” These three short, seemingly simple, words exhibited distinct linguistic features associated with African-American ways of speaking.

First was the rendering of “no” as “nah.” The vowel sound in “no” is like the one in “note,” while the vowel sound in “nah” is like the one in “not” (not to be confused with the way some whites say “nah” as in “gnat,” or the way some Southerners say “naw” like the vowel sound in “gnaw”).

Second was Mr. Obama’s use of “straight” in the sense of “O.K.,” “fine,” “all right.” Observers have noted Mr. Obama’s use of black slang in relation to hip-hop culture, his use of words like “flow” (the mapping of rhymes onto a beat) or “tight” (cool, hip). In his memoir “Dreams From My Father,” Mr. Obama also used words and phrases that are not as widely known outside the black community, like “trifling” (lazy and inadequate) and “high-yella” (a reference to light-skinned blacks).