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The positive or negative slant to a given word or word phrase is refered to in linguistics as its semantic orientation. For example, "pungent" and "fragrant" mean essentailly the same thing, i.e. "odorous," but the first has a negative semantic orientation, the latter has a positive one. Another way to understand it is that antonyms express opposite semantic orientations to the same core concept.

Orientation is not fixed and is often dependent on context. For example, "unpredictable" might be negative in an automotive review, e.g. "unpredictable performance", but might me positive in a movie review, e.g. "unpredictable plot." Even the speaker of a given term can change the listener's orientation, as is the case with derogative epithets.

Cultural sidenote: Americans can indicate disagreement with the apparent orientation of a word using scare quotes, aka air quotes, e.g. "The only <scare quote>problem<scare quote> here is your attitude, officer."

The term was coined by Elder Olsenin, in On Value Judgements in the Arts and Other Essays, 1976.

Though semantic orientation has long been the interest of poets, translators, critics, philosophers, and defense lawyers, it is of recent interest to computer scientists because in the age of the Internet, such particular data mining can be automated. For the first time, texts are available in a huge variety of websites and databases in a computer-searchable form. And while Google can provide 41,700 search results for "Ivrea, Italy", it would still take a significant effort on the searcher's part to skim any significant portion of these results to determine if, in general, Ivrea was regarded as a good place to visit. (Incidentally, I'd say yes just before Lent.) If you could teach a computer to correctly assess whether the texts associated with Ivrea were positive or negative, then you could provide a general summary with the search results.

Obviosuly, such information is of keen interest to individuals or organizations keeping tabs on their popularity, such as politicans and entertainers. Companies are also interested in the public orientation toward their brand. In fact I'd hazard that anyone with a presence on the Web is probably interested when they're ego surfing. Searchers for information may be interested in neutral sources, or if they are proof texting, sources with a particular slant.

As the more and more of human communication is recorded and computerized this data will be more and more available, and what’s creepier, accurate.