The logical positivists led by Carnap led the charge against metaphysics and ultimately failed. From the IEP article on Carnap:
He asserted that many philosophical problems are indeed pseudo-problems, the outcome of a misuse of language. Some of them can be resolved when we recognize that they are not expressing matters of fact, but rather concern the choice between different linguistic frameworks. Thus the logical analysis of language becomes the principal instrument in resolving philosophical problems. Since ordinary language is ambiguous, Carnap asserted the necessity of studying philosophical issues in artificial languages, which are governed by the rules of logic and mathematics. In such languages, he dealt with the problems of the meaning of a statement, the different interpretations of probability, the nature of explanation, and the distinctions between analytic and synthetic, a priori and a posteriori, and necessary and contingent statements.
On the surface, there seems to be a clear distinction between statements regarding, say, the arguments of physicists who debate and explore questions of mass, matter, and energy, and those of say, theologians debating angels dancing on the head of pin. Matter, for instance, even though it is beyond direct observation is open to operational definition, where as angels are not. This is because, to a positivist of any flavor, a posteriori that express empirical truths based on objective empirical evidence are held supreme. Thus, Carnap the ontologist was attempting to further realism by defending just what existential quantification entails. He noted that some questions are internal and others are external. External questions revolve around publicly available information such as 'how many legs does an ant have?' versus internal questions like 'what exactly is the nature of the material?'. Carnap maintained that the internal and external referred to the framework of language, and that questions that were internal were pseudoquestions, not proper questions, on the basis of his belief about the analytic-synthetic divide, an idea later challenged by Quine in his Two Dogmas.
This view, that linguistic frameworks were at the center of the debate of what was scientific and what was metaphysical was a furtherance of the linguistic turn, because it chiefly asserted that philosophical discourse was best grounded as an understanding of language, thus continuing the Fregean obsession with meaning grounded in truth as a means of determining semantics. Thus, the logical positivists as a whole asserted that metaphysics was essentially the use of language that ultimately provided meaningless statments, since meaning was rooted in the correspondent theory of truth, that is with a reflection of the state of affairs in the physical world. Internal questions, in this picture, are therefore meaningless because they don't correspond to states of affairs at all. This is called today deflationary ontology because it essentially attempts to eliminate many abstract objects.
What Carnap and others then attempted to do is say that external questions start with observable statements, that is empirical statements that are vested in the senses. However, there are abstractions present in science, and those abstractions may be part of theoretical statements, hence embracing a duality. Then based on observation and theoretical statements in conjunction with correspondence rules, it should be possible to sort out the meaningless metaphysics from the scientific statements. This system was called Ramsey sentences which was a model of how the scientist should be able to discriminate in theory observation statements based on explicit definitions. Thus, a scientist could look at the semantics of a statement and determined where it fit in these classes of statement types. Ultimately, this program failed because it was asserted and then accepted that even perception itself is theory-laden, and therefore the line between internal and external, just like the line between analytical and synthetic propositions is ultimately blurred. Down the road, the ordinary language philosophers, who accepted the inevitability of metaphysical discourse, continued the tradition at looking at "non-ordinary" uses of language which is not an attack on jargon, but rather how some philosophers, such as Hegel, use ordinary language in extraordinary ways which ultimately causes confusion, a belief shared with the logical positivists.
