I want to thank my friend, Marco Ruffino, for his thorough and thought-provoking book on Contingent A Priori Truths (Springer, Switzerland, 2022). I’m especially grateful to him for his interest in my own work on the topic. Here I will present a rejoinder of sorts to Marco’s critique of my own criticism of Kripke’s case for the contingent a priori.

In Naming and Necessity (N&N), Kripke famously provided examples of statements that, he argued, are contingent a priori, in the sense that their semantic content (the proposition expressed) is a priori (in something like the traditional sense) despite being metaphysically contingent. Kripke’s examples arise from the introduction of a name or term into the language (or idiolect) through fixing its reference, i.e., through stipulating its designatum, by means of a definite description. He focuses on three examples, one of which (N&N, pp. 54-57) is

M: Stick S, if it exists at t, is exactly one meter long at t.

It is understood that M in particular is to be considered in the context of a speaker having introduced the term “meter”, as a term for a unit of distance, by means of the definite description “the length of stick S at time t”. Kripke’s arguments persuaded the philosophical community, me included, that these statements are indeed contingent. However, several philosophers, me included, have argued that the examples are a posteriori rather than a priori.¹

Throughout the remainder of this comment, I’ll assume that t is the present time and will suppress explicit reference to it as “t”. Instead, I’ll let present verb tense do the work of referring to the time in question.

I take it that a true statement is a priori iff where p is the proposition expressed, it is humanly possible to know p independently of any reliance on experience and instead entirely through rational reflection (such as is employed in the proof of a mathematical theorem). My own case for the aposteriority of M-which I presented in Frege’s Puzzle, and which borrows from observations by Alvin Plantinga and Keith Donnellan-is straightforward: The proposition p expressed by M, we may suppose, is of the form: the length of S is , where is the length, one meter. This proposition p is such that to know it at all is to know of the length , de re, that S, if it exists, is exactly that long. But the de re knowledge concerning , that S is that long, is paradigmatic of knowledge that is unattainable entirely through rational reflection and can be acquired only through experience involving S.

Marco points out (p. 52) that direct perception of S is not required to gain knowledge concerning S and its length. Suppose for example that S is contained in, and so hidden from sight within, a box of 40 inches in length. Then by looking at the box under the right circumstances, though one does not see S one can nevertheless glean that S is less than three yards in length.

The foregoing establishes that direct perception of S is not a necessary condition for gaining knowledge of an upper bound on S’s length. Building upon insightful observations made by the 18^th Century Irish empiricist Bishop George Berkeley, in the voice of his alter ego Philonous, Marco points out that direct perception of S is also not a sufficient condition for gaining certain knowledge about S and its length. There is a familiar warning label on auto side mirrors: “OBJECTS IN MIRROR ARE CLOSER THAN THEY APPEAR”.

I learned the expensive way (to the tune of Brazilian R$3,000 in auto body repair) that objects in the rear-view video of my Tesla also appear farther away than they are. Likewise, objects can appear larger than they are, and they can instead appear smaller than they are. Seeing stick S in maximally misleading circumstances might give one the erroneous idea that S is several yards in length, or a mile long, or only a few inches. Marco argues that these Berkeleyinspired considerations spell trouble for objections like my own to Kripke’s contention that M is a priori. For one can gain de re knowledge concerning S’s length without seeing S; furthermore, seeing S can leave one with an erroneous impression, and hence a lack of knowledge, concerning S’s length.

It is important to draw a subtle but significant distinction between two sorts of de re knowledge involving S and its length:

The former is de re knowledge of the stick S; it need not be de re knowledge of the stick’s length. The latter is de re knowledge of a particular length (one meter); it need not be de re knowledge of anything like S that is of that length.

In Marco’s case of seeing the box without seeing the stick within it, the observer may know of S that it is less than three yards in length, without thereby knowing how long S is. In particular, the observer does not know of the length, one meter, that S is exactly that long. Furthermore, as Marco acknowledges, the observer’s knowledge of S that it is shorter than three yards (if there is such de re knowledge) is clearly a posteriori. Perhaps the knowledge of the lengths, one meter and three yards, that the former is less than the latter, is a priori. Even if it is, this is not knowledge concerning any particular object having either length. In particular, whereas it is knowledge concerning S’s length-one meter-it is not knowledge concerning S itself.

There are special cases in which the distinction between (i) and (ii) collapses. The knowledge concerning the length, one meter, that it is the length of S and the knowledge concerning S that it is exactly that long are basically one and the very same piece of de re knowledge. It is knowledge both concerning the stick and concerning the length-the de re knowledge that the latter is the length of the former. This is the knowledge expressed by sentence M. It seems clear, at least it seems clear to me, that knowledge of the stick and of the length, that the former’s length is the latter, cannot but be a posteriori. Perhaps one can have de re knowledge of S without seeing S directly. Even if that is possible, it seems clear that knowledge of both S and its length, that the latter is the former’s length, is not even in principle knowledge that can be gained (i.e., the belief epistemically justified) independently of all experience-as in the manner that one knows a theorem by means of a mathematical proof from the Peano postulates. The prospect seems outside the realm of genuine possibility.

Marco objects that “the abstract length with which one establishes a cognitive relation changes according to the perspective under which one sees S” (p. 59). This may be the crucial place where my friend and I disagree. I am prepared to allow that the abstract length may appear differently according to the reference-fixer’s perspective. But I maintain that, at least under appropriate circumstances, it is nevertheless the very same length that the reference-fixer sees, despite its differing appearance. Seeing S and its length under appropriate circumstances is typically sufficient to give one de re knowledge of the stick and its length, that the latter is the length of the former, regardless of any perspectival differences in appearance. Something exactly analogous is true with de re belief regarding more familiar objects. The de re belief that Ralph forms upon seeing Ortcutt with his face concealed beneath the rim of his brown hat is of the very same thing as the belief that Ralph forms upon seeing Ortcutt proudly sporting his thong bikini on Copacabana Beach.

More to the point, (as I said in “How to Measure the Standard Metre”, at p. 205) “some sensory experience in which S plays a crucial role seems to be required” for the reference-fixer to gain the knowledge that S is exactly that long (one meter).

Marco goes on to argue (p. 62) that what is crucial to the epistemic justification of the reference-fixer’s belief that S is one meter long is not the sensory experience of S but the verbal stipulation concerning the measurement word “meter”. I maintain that the verbal stipulation is ultimately irrelevant to the epistemological status of M-the issue of whether it is a priori or a posteriori-and concerns instead the epistemic justification for the meta-truth that M is a true sentence. This is a broader issue that we might want to take up in discussion.

For now, I thank you for your attention and your patience.²