*N. B. – The following is an off-handed rant and will likely include some arguments that may be made in a less-than-clear fashion. This is a topic which is of intense interest to me so PLEASE post any questions, comments, or arguments (pro or contra) in the comments.*
In his book Language, Truth, and Logic, the British philosopher A. J. Ayer puts puts forth a modified version of the weak verifiability thesis. Essentially, Ayer says that any statement about which empirical evidence cannot be gathered and which is not a tautology is nonsense. In other words, there are three classes of statements: 1.) Statements of fact (i. e. statements about which evidence can be gathered via sense data). 2.) Tautologies (i. e. statements which denote equality of two things or concepts). 3.) Nonsensical statements which may be grammatically correct, but don’t actually signify anything.
After explicating his thesis (of which I’ve given only a very brief description here), Ayer goes on to use as a switch to woodshed a bunch of popular metaphysical notions. Monism versus Pluralism? Both positions are senseless because they can’t be empirically verified or refuted. Realism versus Idealism? Neither position is wrong because both are nonsense.
Where I begin to quibble with Ayer, however, is that he tries to tar questions of ontology with the same brush as the rest of metaphysics. In essence he says that statements about the nature of Being (he capitalizes it in his book, possibly to take a swipe at Heidegger) are inherently senseless since no experiential evidence could possibly support or refute them. This position to me seem specious. At first blush, if, as he’s claiming, all metaphysics is comprised of non-sensical statements, then so too must be ontology. And he makes a compelling argument regarding other metaphysical issues. I would argue though that questions of being are of a substantially different kind then, say, questions of substance.
Take, for instance, Heidegger’s work on the relationship between Dasein (i. e. that being for which its own being is an issue) and time. Heidegger argues that time is the horizon of being and reality and that without it, the sort of being that we, as human beings have, would be impossible. While Ayer might be quick to point out that simply proving this logically from axioms is useless if the axioms are incorrect, I would argue that even working with Ayer’s own tools, such ontological claims can be evaluated. We can find sense data to support or refute ontological claims like the one Heidegger is making.
Take, for instance, motion. Motion invariably has two components, a locative and a temporal component. Without either the experience of motion would be impossible. Human beings experience motion. This tells us two seemingly trivial but exceptionally vital things: namely that place and time are real, meaningful concepts with ties to the world of our experiences.
That we experience motion, then, is a piece of evidence (a necessary piece, though certainly not sufficient) which pertains to Heidegger’s comments regarding Being. This means that we can gather evidence in support or refutation of Heidegger’s ontology. Therefore, by Ayer’s own version of the verifiability principle, Heidegger’s ontology isn’t the nonsense that Ayer wants to claim it is, but rather an empirical, evaluatable statement about the world.
This, at least to me, shows that Ayer is wrong on at least some Ontological claims.