Let’s call verificationism the thesis that the meaning of any sentence expressing a synthetic proposition is just its method of empirical verification. It follows that a statement is meaningless if it has no method of empirical verification, and if neither it nor its negation is an analytic truth. (Obviously, this characterization of verificationism could be fleshed out, and most if not all verificationists would refine it in some way.) Empirical verifiability (or falsifiability – I’ll henceforth refer to the former term for ease of explication) is a matter of a proposition’s having some sort of probabilistic or deductive relationship with observable states of affairs. For example, a statement regarding the existence or behavior of an unobservable entity can still be empirically verifiable if it entails or has some sort of probabilistic relationship with observable states of the world (see, for example, Ayer 1952: 13, 38; Carnap 1936: 425-427). Thus, a statement about, say, an atom, can be empirically verifiable if it is evidentially related to observation sentences – things like “under such-and-such conditions the cloud chamber will look like this,” or “under such-and-such conditions the screen connected to a scanning tunneling microscope will look like this.” Alright, here’s my question: what does the verificationist mean by “observable” and “unobservable”? Or, more specifically, because these are the terms the verificationist is more likely to use, what does the verificationist mean by “possibly observable” and “possibly unobservable”?
Maybe the verificationist will say at this point that what we should mean by “possibly observable” is “nomologically possibly observable” – possibly observable, given the actual laws of nature (this view is maintained by many positivists, e.g., Carnap 1936: 423). Here is the problem with this response. Galileo is said to have dropped two cannon balls of different weights from the leaning tower of Pisa to see if one fell faster than the other (they both fell at the same rate). But shouldn’t the verificationist concede that the following statement is meaningful? “Galileo dropped the cannon balls and the heavier one fell faster than the lighter one.” But apparently the verificationist can’t say this statement is meaningful, because it does not represent a nomologically possible observable state of affairs.
Ayer, A. J. Language, Truth, and Logic. 2nd ed. New York: Dover Publications, 1952. Print.
Carnap, Rudolf. “Testability and Meaning.” Philosophy of Science 3.4 (1936): 419-71. Print.