A long recognized problem for linguistic theory has been to explain why certain sounds, sound oppositions, and sound sequences are statistically preferred over others among languages of the world. The formal theory of markedness, developed by Trubetzkoy and Jakobson in the early 1930's, and extended by Chomsky and Halle (1968), represents an attempt to deal with this problem. It is at least implicit in that theory that sounds are rare when (and because) they are marked, and common when (and because) they are not. Whether sounds are marked or unmarked depends – in the latter version of the theory, particularly – upon the ‘intrinsic content’ of acoustic and articulatory features which define them. There was, however, no substantive attempt among early proponents of the theory to show what it was about the content of particular features and feature combinations that caused them to be marked, and others not.