Sentence:  The route from the desire for rationality via the desire for objectivity to descriptivism is a well trodden one; but it is nevertheless a <WSD>primrose path</WSD>; for, as we shall see, it leads those who follow it into one or another form of relativism, which is precisely what these thinkers are trying to avoid. They can only avoid it by retracing their steps. / This <WSD>primrose path</WSD> starts from the assumption that the only way to achieve rationality is to secure objectivity. 
Meaning of the word marked with <WSD> tags:  A deceptively easy or appealing course of action that leads one astray or into error.