In my last post I replied on behalf of the ‘modal necessitarian’ to Schaffer’s arguments in the first half of this paper. In this post I’ll have some things to say about the second half of the paper: Schaffer’s response on behalf of the quidditist to the anti-quidditist’s epistemological argument.
Quidditism, as Schaffer uses the term, is the acceptance of merely quiddistic differences between possible worlds; that is, it is the view that there are at least two distinct worlds ‘that differ solely by swaps of which properties confer which powers’. Anti-quidditism is the denial of quidditism.
Why be a quidditist? Schaffer offers an argument from properties (that our best theory of the nature of properties allows them to be repeated across worlds) and an argument from duplication (that the thesis that qualitative duplication is intrinsic depends on quidditism). I will not have much to say about these arguments here.
Why be an anti-quidditist? The motivation Schaffer considers is an epistemological one. Here is the argument laid out in full:
22.1) If there are worlds that differ solely over which property confers which power, then there is a world w distinct from actuality solely over which property confers which power;
22.2) If there is a world w distinct from actuality solely over which property confers which power, then we cannot discriminate between actuality and w;
22.3) If we cannot discriminate between actuality and w, then we do not know whether actuality or w obtains;
22.4) If we do not know whether actuality or w obtains, then (since actuality and w differ over which properties exist) we do not know which properties exist;
22.5) Therefore: If there are worlds that differ solely over which property confers which power, then we do not know which properties exist.
23) We do know which properties exist;
24) Therefore: there aren’t worlds that differ solely over which property confers which power.
Schaffer’s response to this argument, in a nutshell, is to assimilate it to general sceptical worries, for example to external-world scepticism. It’s certainly easy to generate a an analogous argument:
32.2) If there is a world w that contains people in exactly our phenomenal situation who have no hands, then we cannot discriminate between actuality and w;
32.3) If we cannot discriminate between actuality and w, then we do not know whether actuality or w obtains;
32.4) If we do not know whether actuality or w obtains, then (since actuality and w differ over whether we have hands) we do not know that we have hands;
32.5) Therefore: If there is a world w that contains people in exactly our phenomenal situation who have no hands, then we do not know that we have hands.
33) We do know that we have hands;
34) Therefore: there are no worlds that contain people in exactly our phenomenal situation who have no hands.
Although the metaphysical possibility of zombie scenarios may be controversial, the metaphysical possibility of radical sensory error seems pretty secure. So 34 is unacceptable; so either 33 or one of the 32.x premises has to go.
Skeptics, of course, reject 33. Different non-skeptical theories of knowledge might give different diagnoses about which of the 32. premises is the culprit. Dogmatists deny 32.2 or 32.3. Contextualists typically reject 33 in skeptical contexts, and 32.3 in non-skeptical contexts. Anti-closure theorists deny 32.3 or 32.4. Contrastivists say that 32.4 has a true reading and a false reading, depending on how we fill out the contrast class. What all these responses agree on is that 34) should not be rejected as a result of the skeptical argument. But that is the analogous response to the response the anti-quidditist recommends we make to their epistemological argument concerning quiddities.
Schaffer accordingly concludes that the epistemological argument against quidditism is a failure. An exactly analogous line of reasoning would lead us to external-world skepticism; and any strategy for defending external-world realism can equally be applied to defend quidditism against the quiddity-skeptic.
I want to question this response.
We should be alert to the risk of equivocation over ‘quiddistic knowledge’. Certainly, we can have knowledge that there are quiddities, at least according to many of the theories Schaffer outlines. We can discriminate between worlds with quiddities and worlds without – because metaphysics might just crash in worlds without. And it obviously does not crash in ours. Or at least, that seems to be something like the Lewisian line of thought.
But knowing that there are quiddities (derived, perhaps from knowledge that there have to be quiddities) is not the same thing about having knowledge about individual quiddities – knowledge that some particular property has some particular quiddity. Lewis takes it that the former sort of knowledge is accessible by a priori reasoning, but argues at length against the possibility of the latter sort.
The key point is that the epistemological objection to anti-quidditism needs only the latter sort of ignorance. An epistemic situation vis-a-vis quiddities such that we could know that some quiddity or other was present, but never know which, is an unacceptable one; or at least, many people have been unwilling to follow Lewis in biting this bullet.
Schaffer shows every sign of wanting to capture the stronger, which-is-which sort of knowledge of quiddities. The problem is that several of the anti-skeptical strategies he outlines start to falter at this stage. The reason is that it seems impossible to specify any reliable method for gaining which-is-which knowledge of quiddities.
This is most obvious in the case of reliabilist anti-closure theories. They get round the skeptical challenge to external-world knowledge by positing that sense perception is in fact a reliable way of coming to know what the external world is like. But there is no analogous story for our which-is-which knowledge of quiddities. Scientific evidence is evidence only for the Ramsey sentence (let us assume); and sensory evidence is continuous with scientific evidence. Without some Godelian extra-sensory perception of quiddities, it seems that we cannot maintain that we have a reliable route to which-is-which knowledge of quiddities.
Schaffer mentions, with apparent approval, direct realist theories according to which we become acquainted with quiddities directly in the act of sense perception. This is indeed, I think, the most promising line for a quidditist to take. It was Russell’s view: hence his thesis that we know all and only the quiddities of the properties which we encounter in sense perception. The other quiddities we can know only though description – ‘the quiddity of electronhood’. Perhaps some will find a stable resting place here. But this view invokes an unattractively sharp theory/observation divide, and still renders the vast majority of quiddities unknowable in the desired sense.
In sum: even granting that there are quiddities, the quidditist has given no positive proposal about how we acquire knowledge of the quiddities. Herein lies a significant difference with the case of external-world scepticism – it is part of our current best theory that we have a faculty of sensory experience, which in fact usually provides a reliable method for coming to acquire knowledge that we have hands. We thus have a naturalistic story about how we acquire our knowledge that we have hands. Nothing of the sort is available to the quidditist – or at least, all such stories are highly controversial and Schaffer shows no signs of willing to embrace them.
The project of defending a type of knowledge from the sceptic presupposes that we already have well-grounded knowledge of it in non-sceptical contexts. But that is not the case when it comes to quiddities. Nowhere in our everyday or scientific epistemic projects do we actually acquire knowledge that some particular quiddity is instantiated by some particular property. We can get at them by definite descriptions such as ‘the suchness of red’ – but it is not clear that we are talking about anything other than qualitative character of experiences of red.
My preferred way of putting the epistemological argument against quidditism is that of John Hawthorne. Schaffer quotes Hawthorne: “We don’t need quidditative extras in order to make sense of the world… Why posit from the armchair distinctions that are never needed by science?” This way of putting pmatters makes sure that the burden of proof is in the right place. It is the quidditist, with their infinitely-many extra merely quiddistically different possible worlds, that needs to convince us that their extra ontology should be quantified over in our best total theory. (Call a world a world, or dress it up as primitive ideology – it comes to the same thing, in that it adds to total theoretical complexity.)
It seems that worlds differences between which make no phenomenal difference are not needed in our system-of-the-world. There are two ways that the quidditist could respond. The first is to give a non-trivial epistemological story about how we discriminate between different quiddistic possibilities. This is likely to involve direct perception of some sort, I suspect. The second is to insist that objects must have quiddities, and that we must be able to know that they do, but that we do not need to be able to tell which quiddity is had by which property. That leaves us back with the view of David Lewis and, roughly, of Immanuel Kant. If this is where we end up, we should take another look at our motivations for believing in quiddities in the first place. Would metaphysics really crash without them, as Lewis and Schaffer imply?
There is reason to think that quidditism and haecceitism ought to be given a uniform treatment. Those like Adams, who are full-blown haecceitists and full-blown quidditists, have a consistently-motivated, if implausible, position. An anti-haecceitist anti-quidditist has a remarkably austere ontology – one which could perhaps be exhaustively specified by a space of possible mathematical structures and an ‘is physically realized’ primitive. But the positions in-between – the anti-haecceitist quidditists such as Schaffer and Lewis, and the haecceitist anti-quidditists such as, perhaps, Hawthorne – seem to me to be unstable positions.
One lesson is about how metaphysicians skeptical (in the ‘unconvinced’ sense) should approach epistemological arguments against their targets. Don’t tacitly tively grant the possibility of knowledge about your subject, and then seek to undermine it by indiscriminability arguments. We have plenty of lines of defence against those arguments and – while none of these lines of defence ought to work out to deliver knowledge of entities that do not in fact exist, it may not always be obvious that they fail. We are dealing with some potentially faulty theories of knowledge. Are we so sure that every one of the pictures of knowledge Schaffer adduces are coherent and fully tenable positions? If not, why think that some theory’s ability or inability to refute a particular sceptical argument isn’t due to a problem with the theory?
The subtleties of the way different theories of knowledge cope differently with our epistemic position vis-a-vis particular metaphysical posits are liable to be a distraction. If there really is methodological reason to avoid positing quiddities, we shouldn’t need to check how this pans out with each and every theory, and particularly not with the more controversial ones.
I think what are often called ‘epistemological’ arguments in metaphysics are often better construed as methodological arguments. Very often, we find employed conditionals of the form ‘if theory T were right, there would be a distinct range of facts unknowable by us.’ the conclusion is drawn that this is a regrettable thing to suppose. It is better to argue thus: ‘T undermines its own motivation, for the facts it invokes to explain the phenomena are in fact incapable of doing the job.’ This form of methodological argument for eliminativism, I think, can help us dispense with quiddities, haecceities, absolute simultaneity, absolute actuality, God, and much else besides.