Logical Positivism emerged in the early 1920's. The movement is an outgrowth of a radical version of British Empiricism. Logical Positivism was built around the principle of verification in which adherents argued that the only meaningful statements of truth are those, which are empirically verifiable. According to the Logical Positivists, a statement is meaningful if it meets at least one of two criteria:
1) It is based on sense data or experience (empirical observation).
2) It is a "linguistic convention" or "tautology" meaning that it is a truth the meaning of which is determined by definition.
Logical Positivism was characterized by the following elements: the verifiability criterion, necessary truth and reductionism.
1) The verifiability criterion of meaning
According to the Logical Positivists, statements about the world must have their source in some reality in the world and, in turn, must therefore be empirically verifiable. Discussion concerning this principle centered upon the significance of the word "verify." On the one hand, extreme verificationism, argued that in order for an individual to make the statement, "There is a table in front of me" there must be empirical evidence of the actual reality of such a statement. However, extreme verificationism was subject to doubt due to the reality that certain apparent truths simply are not verifiable.
Consequently, some verificationists opted for a modified verificationism, which focused not upon certitude but upon probability or likelihood of a propositions being true. Two issues emerge from this modified version of verificationism. On the one hand, modified verificationism was more difficult to disprove than extreme verificationism. On the other hand, however, critics argue that modified verificationism likely fails to meet the original goal of the Logical Positivists which was to rule out truth statements that are, at least in the view of the Positivists, nonsensical.
2) Necessary Truth
Logical Positivism also argued that all truth might be placed in two categories. On the one hand, there are meaningful statements which are necessary truths (a priori analytic statements) and, on the other hand, there are meaningful statements, which are contingent truths (a posteriori synthetic statements).
"All bachelor's are unmarried" is an example of a necessary apriori analytic statement, also known as a tautology. These types of statements tell us nothing about the world and are either true or false based upon some fact about the rules of language. These were necessary truths and according to the Logical Positivists are to be reduced to tautologies. However, as will be seen below, this is problematic for the Logical Positivist.
Logical Positivism experienced significant challenge at the point of necessary truth as well. In short, it is difficult if not impossible in some instances to reduce necessary truth to formal tautologies. For example consider the following frequently used examples of these tautologies:
a) Everything that is blue all over is not red all over.
b) All equilateral triangles are equiangular triangular.
c) No proposition is both true and false.
3) Reductionism
Sense data are themselves neither mental nor physical. The mental-physical distinction consists simply in our organization or arrangement of predicates, for example size, shape, etc. Positivism argues that others minds and even one's own mind are logical constructs since they are not sense nor are they composed of sensory data. The self, in short, is nothing more than a bundle of perceptions and there is no continuous substantial self and theoretical entities such as atoms and average housewives for example, exist only in terms of theories for explanatory and predictive purposes. This is not the first occurrence of such reductionism in epistemology. Locked dropped the idea of innate ideas; Berkeley dropped Berkeley's/Locke's recognition of material substances and causality; the Positivists drop Hume's belief in things in favor of sense data or "phenomena."
