In It’s Not Easy Being Grue, I argued for skepticism — or at least incredulity — towards any inductive inference made solely by appealing to a posteriori evidence. Two hypotheses, as long as they have a logical content greater than the evidence and are not yet refuted are, as a matter of following the rules of logic, necessarily equally favored by the evidence. Even if one should appeal to one of the two hypotheses having a natural property, this problem still stands, since it cannot be uncovered through a posteriori investigation. Of course, more than two hypotheses fit this criteria — any number of empirically adequate hypotheses with greater logical content than the evidence may be constructed. In sum, favoring one hypothesis over another, even with an a prior warrant, cannot be determined from a posteriori evidence at all.
Jessica is different than James. She sees the failure of his program and preemptively seeks out some a priori warrant for favoring some inductive inferences over others. Is there an a priori warrant that would allow Jessica to favor one hypothesis over another? For the time assume that such a warrant exists. Assume that if Jessica finds this warrant, the problem is solved. I will not go into the other problems that face Jessica — whether or not she can know that she has the warrant, whether or not she can know that she knows that she has a warrant, &c.
Some predicates, such as ‘green’ intuitively (so it is said) fit the list of natural properties while others, such as ‘grue’, intuitively do not. Call those grue-like properties ‘ill-behaved’ properties for now. What metaphysical standard sets natural properties apart from ‘ill-behaved’ properties?
We might say that it is solely intuition that guides us; we reject ‘ill-behaved’ predicates like ‘grue’ because they are disjunctive: they involve spatio-temporal properties that, like a cat that turns into a dog after whistling, cannot function within our commonsense ontology. If we assume that we are warranted in rejecting disjunctive predicates due to our intuition, this does not solve the problem, since it begs the question as to why our intuitions are warranted. How then can we give warrant to our intuitions? But first, some historical case-studies:
- We can take ‘leopard’ as not having spots before a certain time, and having spots after that time. Any other ‘Just-So’ story by Kipling is an example of a possible variation on English (call it ‘Kipling-English‘) that takes a number of animals as having a ‘ill-behaved’ list of properties.
- Christians take transubstantiation, the transformation of bread and wine into the literal body and blood of Christ after a specific incantation by a priest, very seriously. The term ‘Eucharist’ is then an ‘ill-behaved’ property that has been ingrained into the English lexicon and the Western mind for almost one thousand years.
- Aristotle took elements to be of two classes: the worldly elements would move linearly towards their natural place unless acted upon, while the heavenly element, known as ‘æther’, was incapable of change other than rotation. Natural motion was then for hundreds of years an ‘ill-behaved’ property as well: just in some cases linear, but in others rotational. It took the work of Newton and others, through imagination, scientific investigation, and questioning Aristotle’s metaphysics, to link these two classes under one unifying force.
Thus, the English language already has several well-established ‘ill-behaved’ spatio-temporal properties in its lexicon. Of course, they are few and far between, so this is far from a convincing argument. It might be said that they’re works of fiction, or strange imaginings, and do not belong to commonsense talk. However, the predicate ‘grue’ is a disjunctive predicate only according to the colors expressed in standard English. If there was an alternative history where all colors were expressed in predicates that are ‘ill-behaved’ in English (call it ‘Engrish’), the predicate ‘grue’ would not be disjunctive or ‘ill-behaved’ in that language; we could not say the same about the predicates ‘green’ and ‘blue’ in Engrish.
It is plausible that, had Engrish been the lingua franca today, we would intuit that any ‘ill-behaved’ property according to English was a natural property, since it did not express a spatio-temporal property, while any natural property according to English was ‘ill-behaved’. Imagine that Jessica and James both decided to base their favoring of one hypothesis over another on their list of (supposed) natural properties. As it so happens, Jessica speaks Engrish and James speaks English. Both Jessica and James see X number of emeralds. Jessica and James both look to their intuitions, and each of them decides that the emeralds are ‘grue’ and ‘green’, respectfully. Each claims that the other is adopting a language that functions with ‘ill-behaved’ properties. How can we decide?
We cannot say that our list of natural properties is obviously true, and choose between Jessica and James on the basis of this list. We are not an outsider with privileged access to the list of natural properties. This would immediately assume the solution to the problem at hand, since like Jessica, we could have been raised speaking Engrish and not English. An accident of birth, rather than a strong metaphysical or epistemological argument, is (as I see it) the only thing that leads to favoring one unfalsified hypothesis over the other.