During the years at the end of the nineteenth and beginning of the twentieth centuries when Saussure was working out his ideas in Europe, synchronic linguistics was emerging independently, and in a very different style, in America under the leadership of the anthopologist Franz Boas set a direction for American linguistics which turned out to be enormously fruitful, and which was never seriously disputed until Noam Chomsky appeared on the scene in the late 1950's.
The Descriptivist tended to think of abstract linguistic theorizing as a means to the end of successful practical description of particular languages, rather than thinking of individual languages as sources of data for the construction of a general theory of language. It is true, of course, that the most eminent of the Descriptivists are well known because, they did theorize about language in general; but in all cases their general theories were backed up by intensive research on the detailed structure of various exotic languages, and many of their less famous colleagues and followers preferred to take the theories for granted and concentrate on the data.
The fact that Boas was a purely self-thaught linguist was an advantage rather than a hindrance in dealing with American Indian languages, since it was necessary in approaching them to discard any presuppositions about the nature of language inherited from a European background. A characteristic of the school founded by Boas was its relativism. There was no ideal type of language, to which actual languages approximated more or less closely; human languages were endlessly diverse, and although the structure of a language spoken by some primitive tribe might strike us as very 'arbitrary' and irrational, there was no basis of truth in such a judgement: our European languages would appear just as irrational to a member of that tribe.