Over the past thirty years or so a number of scholars, mostly but not entirely American, have sought to elucidate problems of genetic linguistics by employing, explicitly or not, some form of probability mathematics. As I reread these efforts, my own included, I wonder that no one has ever seriously questioned the pertinence or, indeed, the legitimacy of such employment in elucidating historical problems. Mathematics takes vaguely defined terms of ordinary speech like ‘probability’ and ‘chance’ and gives them precise meanings, but when we use such terms in linguistics, together with their associated mathematical procedures, do we always keep the precise meaning? Or do we fall back unwittingly into the popular use and thus vitiate our results? And even if we are careful to keep the precise meanings, are we justified in supposing that mathematical probability can furnish a theory to account for the phenomena of history in languages, or, if not a theory, then a model? Such questions as these deserve answers, and by now enough experience has accumulated to warrant an attempt to answer them. The present paper is offered as such an attempt with the hope that, if it does no more, it will at least ask the right questions. But first a word must be said about theories and models.

This paper presents a theory of the child's acquisition of the phonology of his native language. The theory predicts learning, measured by correct pronunciation of phones, as a function of ease of perception. The general prediction is that the more discriminable phones are learned earlier and the less discriminable ones later. Finally, the theory is compared with some previous suggestions in this field.

This paper discusses various types of phonological phenomena, some of the concepts that linguists have employed in dealing with them, and certain questions to which previous work in phonological theory has not provided satisfactory answers. These considerations lead to the recognition of some distinctions heretofore overlooked and to a new theory of phonology, certain features of which are outlined.

This Issue of Language, dedicated to Y. R. Chao, was planned by Bernard Bloch, who began work on it before his death on 26 November 1965. The duties of acting editor were then assumed by Warren Cowgill, who completed the editing and sent the copy to the printer; special thanks are due to him for his devoted service in a difficult time. Finally, the correction of proofs was supervised by the present editor.