As time goes by, it generally softens asperities in the character of men and women from the past. We have quite a cuddly image of Ben Franklin, but to those who met him he could seem truculent and abrasive. Something rather different has happened in the case of Samuel Johnson. He used to be presented as a formidable figure—an overbearing literary potentate, if not a clubroom bore whose table you would avoid in the dining room. People thought him domineering and arrogant, qualities reflected in his nickname “the Great Cham.” Oldstyle British actors gave him a plummy upper-class bark, even though the evidence showed that he spoke with a strong Midlands accent, not too far from the nasal intonation you can hear on the streets of Birmingham today.

It has all changed dramatically in the last half-century. In fact, the shift has its roots even further back, in an essay by an outstanding sc ...