Logical Positivism: Schlick, Carnap, A. J. Ayer

Strongly influenced by the Tractatus of Wittgenstein, a group of philosophers in Vienna in 1920s initiated a movement which came to be known as Logical Positivism, and the group of philosophers became famous as the Vienna Circle. The Vienna Circle was led by Moritz Schlick (1882–1936), the professor at University of Vienna, and other leading members included people like Rudolf Carnap (1891-1970), Otto Neurath and Friedrich Waismann. A. J. Ayer (1910-1989) belonged to the circle as a young man and later became one of its most enthusiastic spokesmen in the English-speaking world.

It is said that Logical Positivism began when Wittgenstein wrote in Tractatus that philosophy is not a body of doctrine but an activity. And this single sentence does summarize the whole of logical positivism. Logical Positivists believed that the purpose of philosophy was not to produce new propositions describing the universe or reality, but rather, the purpose was to analyze the existing propositions to find out whether the statement is mathematical, scientific or nonsensical. The Vienna Circle believed that a significant proposition has to be either a proposition of formal logic or a proposition of science. Any other statement would simply be nonsensical; not true, not false, but nonsensical. If it had any meaning at all, it would be ‘poetic’ or ‘emotive’ but not cognitive. To the logical positivists, “God exists in the heavens” is as nonsensical as “Bong shong in the dock pock.”

The Logical Positivists took up the analytic/synthetic distinction. As we already know, an analytic proposition is one which is necessarily true, because its truth follows from its meaning i.e. it would be self-contradictory to deny it. “All bachelors are unmarried men” is an analytic statement. A synthetic proposition is one which is not analytic and which requires empirical investigation for the establishment of its validity. “All bachelors go to theatre on Saturdays” is a synthetic statement. It might be true, but you can’t tell that just by the analysis of the statement itself. On the other hand, analytic statements do not tell us anything about the world. The statement “The blue pen is of blue colour” despite being true doesn’t tell us whether a blue pen exists in the world or not. But the statement “The blue pen is lying on my desk”, if true, does tell us something about the world. In other words, analytic propositions are trivial but synthetic propositions are informative.

Now the problem arises, how can we tell whether a particular synthetic proposition is significant or not, whether it is meaningful or nonsensical? To answer this, the logical positivists formulated the Verifiability Criterion of Meaning. Any statement which passed this criterion would be significant. If it failed, it would either be analytic, or nonsensical. This criterion has been stated in different ways by different philosophers. Simply, the criterion says that a proposition will be significant only if it is possible to verify or falsify that proposition by observation. If an observation could be described which would show whether the proposition is true or false, then the proposition is significant, otherwise it is meaningless. For example, if a person claimed that the universe and everything in it is expanding uniformly, such that all our standards of measurement are also expanding uniformly along with it, then there is no possible way by which we can actually find out whether this is true or not. All the people, all the buildings, all the planets would have expanded in the same proportion, so there would be no observable difference at all. If you wish to measure the length of an iron rod which is expanding, and simultaneously the measuring rule is expanding in the same proportion, then there is no way that you can measure the increase in the length of the iron rod using that measuring rule. That is to say, a statement like “The universe is expanding uniformly” is meaningless.

Here it would be important to note that in order for a proposition to be significant, it has to be verifiable in principle, not in practicality. For example, it is not possible at the moment to verify the statement “There are little green men living on Mars” because we have not gone to Mars yet. But, it is possible in principle to verify this statement. We can describe the conditions under which this statement would be true or false. If we send a mission to Mars and the astronauts find little green men living there, then the statement would be true, and if they do not find any little green men, then the statement would be false. In either case, the statement is significant. But is there any possible way by which you can verify the statement, even in principle, that “God exists in the heavens”? No, there isn’t. So the statement is insignificant.

The implications are, of course, disastrous for the traditional philosophy. Because the propositions of ethics, metaphysics and theology are not verifiable by experiments, hence they are either trivially analytic or they are nonsensical. And so, the logical positivists claim, the purpose of philosophy is to not make statements about the nature of reality; that is the purpose of science. The purpose of philosophy is to analyze a problem, and to show that either it belongs to logic and mathematics, or it belongs to science, or it is altogether insignificant. But to solve these problems is not the task of philosophy.

The biggest problem faced by logical positivism has been that it has never been possible to explain the verifiability criterion, which is central to the whole logical positivism, accurately enough to describe where exactly science ends and metaphysics begins. There have been repeated attempts and repeated failures in trying to draw the line at the ‘right place’. And then, the logical analyst W. Van O Quine has shown that the distinction between analytic and synthetic propositions is no longer valid, and that this distinction is more of a convention than an intrinsic division between the propositions. Garth Kemerling writes, “Quine has argued that no strict distinction can be maintained, since the analyticity of any proposition can be denied, with suitable revisions of the entire system of language in which it is expressed.”[1] Due to these reasons, logical positivism lost its influence by the 1960s.


[1] Garth Kemerling, Philosophy Pages,