What happens when a familiar word meets a genuinely new case—and neither “yes” nor “no” feels like a mistake? This paper argues that the discomfort may reveal a distinctive feature of language, not merely ignorance or vagueness. Established ways of talking can be unsettled by new developments, particularly when features once presumed to co-occur diverge.

This observation underlies a group of cases familiar from the mid-twentieth century, particularly the work of Friedrich Waismann, a one-time collaborator of Ludwig Wittgenstein. Waismann imagined discovering a metal that shares all of gold’s properties save its spectral profile.

The case is meant to leave us stymied, even though spectral profile had the classificatory significance that atomic number does today. The underlying possibility is that an unforeseen situation could arise in which a definition would have to be modified. These cases were taken to undermine a verificationist criterion of meaning and to reveal the open texture of concepts.

The intuition is that no finite description of the relevant observations entails that some substance is gold. Given any list, a conceivable scenario could introduce a further property that seems to bear on whether the term applies. The point is supposed to concern linguistic meaning, but exactly what it amounts to is not clear.

The eBook case asks whether eBooks were in the extension of “book” as used before the digital age. Purchasing an eBook involves acquiring a license to a digital file readable on an electronic device. Today, eBooks might be felicitously classified as books, and just as felicitously distinguished from them.

When someone asks, “Did you pack your book?”, both charging the eBook and mentioning an eReader without batteries are acceptable responses. The rape case asks whether forced sex within marriage was in the extension of “rape” as used in nineteen hundred in non-legal discourse.

Some legal systems recognized marital rape in cases of estrangement, although standards of proof were very demanding. In the seventeenth century, Matthew Hale denied that a man could rape his wife because sexual consent was given at marriage. That conclusion was received in common use as quasi-definitional and persisted in law and popular thought in many jurisdictions until activists challenged it in the nineteen seventies.

The ruby case asks whether the Black Prince’s Ruby was in the extension of “ruby” as used in seventeen hundred. Balas rubies and true rubies had been distinguished, but both were judged to be rubies, unlike garnet. Around eighteen hundred, these stones were discovered to be two distinct minerals: red spinel and red corundum, or red sapphire.

Soon, “ruby” was restricted to the latter, while spinel, including the Black Prince’s Ruby, became known as the “Great Imposter.” The planet case asks whether Pluto was in the extension of “planet” as used before two thousand four. By the early two thousands, astronomers had identified many Pluto-like trans-Neptunian objects, including at least one more massive than Pluto.

The International Astronomical Union tasked a committee with producing a working definition of planet. In two thousand six, a proposal was adopted that included the provision that planets clear their orbits, and Pluto was reclassified. Some open cases classify something new, like NUMBER and BOOK, while others reclassify something familiar after new developments, like RAPE, RUBY, and PLANET.

Both kinds can look like theory change, because both prompted reassessment of the statements that marked speakers as competent with the relevant predicate. They can also look like vocabulary change, but calling the first conceptual extension and the second conceptual sharpening merely redescribes an apparent difference.

Introducing new words would only push the question back onto whether those new words applied to what had previously been called numbers and rubies. Open cases elicit the sense that answering the leading question reveals something about what speakers have been talking about all along.

This sense motivates, or perhaps just is, a pattern of judgments called continuity judgments. Continuity judgments include applying or withholding a predicate in new cases and reassessing past utterances, including “There are nine planets” and “All numbers fall on the number line.”

People routinely apply the inference schema “something is F, so it is F” to past utterances and texts, as when Carl Sagan’s statement about planets supports the same conclusion. This pattern of judgment often goes unremarked in discussions of open cases, even though it features prominently in descriptions of them.

Cases with unstable reactions and continuity judgments give rise to puzzles of fission and sequential change if they are treated as indicative of meaning. Unstable phenomenology raises the possibility that usage could diverge in isolated linguistic communities.

Continuity judgments raise the possibility that later speakers regard their usage as synonymous with the pre-divergent usage, but not with usage in the other divergent community. The simplest version of these puzzles is an inconsistent triad. The first claim is supported by the International Astronomical Union’s pre-two-thousand classifications and by dumbfounded or conflicting dogmatic reactions to new observations.

The second claim is supported by the International Astronomical Union’s current classifications. If the first and second claims are both true, the third claim, read de dicto, appears to be false. If contemporary uses of “planet” express an intension different from the one expressed before two thousand four, humanity has only recently entertained thoughts about new planets.

A treatment of Waismann-like cases does not explain why they elicit dumbfounded or dogmatic reactions, or why those reactions still seem more or less appropriate for past speakers. The gold case at most shows that the metal gold cannot have deviant spectrometry, but that alone does not explain what this tells us about the meaning of “gold.”

Rigid designation struggles to provide a compelling analysis of non-science-fiction cases. Even ostensive definitions may depend on an implicit description or empirical presupposition that can fail, and causal chains transmitting reference may be subtly disrupted.

The analysis considers three ways to attribute the dumbfounded reaction and openness to ignorance. The first two concern ignorance of the future, while the third concerns the obscurity of meaning determination. The subsequent sections ask whether openness is some more familiar semantic phenomenon.

A natural thought is that open cases stem from indecision rather than ignorance about the environment or the future. Language users have not, and perhaps cannot, make all the decisions needed to fully determine extensions. An expressivist account of vague predicates treats borderline cases as practical uncertainty about whether to treat something as F, with the issue being whether that treatment is correct rather than whether it is true.

The remaining question is whether openness is one of several familiar linguistic features, including semantic incompleteness, vagueness, non-vagueness indeterminacy, or pragmatic underdetermination. If the open cases are unified, openness is not a matter of being partially defined.

Analyzing RUBY, RAPE, or PLANET as incomplete overlooks that the predicates were taken to be complete in the relevant respects at the time. What is now described as marital rape was once taken to fall within the anti-extension of rape, not a gap.

If “ruby” was partially defined with respect to the stones it was believed to apply to, there might simply have been nothing properly called a ruby. Openness differs from vagueness in ways that suggest they are different phenomena.

Vagueness tends to elicit equivocal responses together with agreement that equivocality is appropriate, as in a quarrel about whether Jim is bald. That reaction differs from the unstable phenomenology elicited by open cases, including dogmatism.

Shapiro’s context-sensitive account connects borderline cases to Waismann’s notion of open texture and allows a speaker to assert both a predicate and its negation, though not in the same context. Another possibility is to analyze openness as a form of non-vagueness indeterminacy.

One version makes the meaning relation itself indeterminate or partial. Another version says that tokens express multiple determinate meanings, understood as precisifications or latent ambiguity. The cases resemble those once taken to exemplify the open texture of language, and they elicit unstable phenomenology and continuity judgments.

Their features are not obviously well explained by a metasemantic theory or by ignorance of some sort. There are reasons to doubt that the cases stem from partial definition, vagueness, non-vagueness indeterminacy, or contextual or pragmatic underdetermination.

Still, openness can be represented as one of these phenomena for the purposes of a semantics. Open texture is presented as a distinctive phenomenon: its cases produce unstable reactions and continuity judgments, yet resist familiar explanations such as partial definition, vagueness, indeterminacy, and underdetermination.