“(...) We seem unable to differentiate between "compare to" and "compare with". This, from a recent piece about the cricketer Mark Ramprakash, is typical: "Watchers compared the schoolboy with Denis Compton as he smashed the Yorkshire attack around Lord's." This sentence conjures up an image of the watchers, perhaps viewing archive footage of the late Compton, attempting to assess the similarities and differences between the two batsmen. What the watchers actually did was liken Ramprakash to Compton. They said he was just like Compton. They compared him to Compton! How hard is that?
We have similar problems deciding between "who" and "whom". You can bet what's left of the equity in your house that, on one of the rare occasions when we summon up the courage to use the latter, the former would have been correct. It may not matter too much, as "whom" seems to be disappearing from English usage altogether, but it would be nice to get it right once in a while.
As for "that" and "which", my faith in the infallibility of the style guide's formula (which I stole from a former colleague at the Independent) – "this is the house that Jack built; but this house, which John built, is falling down" – is daily tested by a near universal failure of my colleagues to observe the distinction.
Although grammar is often fuzzy and open to interpretation, in my book these three mistakes all come down to a Manichean choice between good and evil, light and dark, right and wrong. If the style guide is no help, perhaps when faced with deciding between "compare to" and "compare with", "who" and "whom", or "that" and "which", we should simply toss a coin.”