In a word: To compare the differences
Mick Hart wants to know the difference between compared with and compared to. I learned this back at university, so I'm going to quote from the classic source that taught me the answer: The Associated Press Stylebook and Libel Manual.
"Use compared to when the intent is to assert, without the need for elaboration, that two or more items are similar: She compared her work for women's rights to Susan B Anthony's campaign for women's suffrage.
"Use compared with when juxtaposing two or more items to illustrate similarities and/or differences: His time was 2:11:10, compared with 2:14 for his closest competitor."
Oxford Concise tends to agree, but one finds it in the definitions given for compare:
(compare something to) liken something to.
(compare with) be similar to or have a specified relationship with another thing or person: salaries compare favourably with those of other professions.
Mr Hart also wanted to know if there was a preference for different to, as opposed to different from.
Oxford Concise has something to say on this issue, too:
"There is little difference in sense between different from, different to, and different than, and all have been used by respected writers. Different from is traditionally held to be the correct structure, and is the commonest in written evidence. Different to is common in Britain, but is disliked by traditionalists. Different than is used chiefly in North America. It has the advantage that it can be followed by a clause, and so is sometimes more concise than different from: compare things are definitely different than they were one year ago with things are definitely different from the way they were one year ago.
The Associated Press Stylebook, on the other hand, is quite succinct: Different takes the preposition from, not than.
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