For all its many virtues, the fifth edition is not perfect. Its one glaring flaw is an introductory essay written by the chairman of the Usage Panel, Steven Pinker, a Harvard University linguist and cognitive scientist who is also an avowed descriptivist. In “Usage in The American Heritage Dictionary,†Pinker writes, “(W)hen many speakers misuse a word on many occasions in the same way — like credible for credulous, enervate for excite, or protagonist for proponent – who’s to say they’re wrong? When enough people misuse a word, it becomes perverse to insist that they’re misusing it at all.â€