This book makes a fundamental contribution to phonology, linguistic typology, and the nature of the human language faculty. Distinctive features in phonology distinguish one meaningful sound from another. Since the mid-twentieth century they have been seen as a set characterizing all possible phonological distinctions and as an integral part of Universal Grammar, the innate language faculty underlying successive versions of Chomskyan generative theory. The usefulness of distinctive features in phonological analysis is uncontroversial, but the supposition that features are innate and universal rather than learned and language-specific has never, until now, been systematically tested. In his pioneering account Jeff Mielke presents the results of a crosslinguistic survey of natural classes of distinctive features covering almost six hundred of the world's languages drawn from a variety of different families. He shows that no theory is able to characterize more than 71 percent of classes, and further that current theories, deployed either singly or collectively, do not predict the range of classes that occur and recur. He reveals the existence of apparently unnatural classes in many languages. Even without these findings, he argues, there are reasons to doubt whether distinctive features are innate: for example, distinctive features used in signed languages are different from those in spoken languages, even though deafness is generally not hereditary. The author explains the grouping of sounds into classes and concludes by offering a unified account of what previously have been considered to be natural and unnatural classes. The data on which the analysis is based are freely available in a program downloadable from the publisher's web site.