Wolfgang Schwarz

Everything is possible

Just when I thought all viruses are specific, I caught an 'unspecific virus' last weekend -- at least that's what the doctors at the hospital identified it as. So I've been knocked out for about a week, but now I'm back with an exciting new theory of modality.

The theory is simple. It says that everything is possible. Pace Kripke, there are possible worlds where Queen Elizabeth is a poached egg and where Hesperus isn't Phosphorus. And pace almost everybody else, there are possible worlds where squares are round, bachelors married and where Hesperus isn't even self-identical.

If it rains

This appears to be a problem for pure epistemic accounts of indicative conditionals (a la Weatherson and Chalmers), on which "if A then B" is true iff the [epistemically] closest worlds verifying A also verify B.

The match cannot be played if it rains; either it has to be postponed or canceled. Which of these will happen is regulated by the rule book, but nobody has looked up the relevant passages so far. All we know is that exactly one of these two conditionals is in the rule book, and therefore true, and the other false:

Against abstract identifications

Some philosophers believe that the second world war is a triple of a thing, a property and a time. Others have argued that my age is a pair of an equivalence class of possible individuals and a total ordering on such classes. It is also often assumed the number 2 is the set {{{}},{}}; that the meaning of "red" is a function from contexts to functions from possible individuals to functions from possible worlds to truth values; that possible worlds are sets of ... sets of properties; and that truth values are the numbers 0 and 1 (aka the sets {} and {{}}).

Diamond Implicature II

I've thought a little more about this thing I called 'diamond implicature', and I've come up with the following explanation. I don't know if it's original, and unfortunately, I don't see how exactly it applies to the antecedent of counterfactuals, which is what I am most interested in.

The explanandum is that in many contexts, appears to imply . For example,

Norms of rationality

My officemate Jens-Christian, my flatmate Weng Hong and his officemate Aidan have started a blog on bunnies probabilitiy, possibility and rationality. There's already a couple of good posts by Weng Hong.

We had a little chat about the normativity of rationality today. Unlike with moral norms, I cannot imagine people who vastly disgree with me on the norms of rationality and who actually act upon their different norms. Can you imagine people who usually infer "~P" from "P and Q", update their beliefs by counter-conditionalizing P'(H) = 1-P(H|E), and always try to minimize their expected utility? I can't. By contrast, I find it easy to imagine people who value torturing innocent people and do so. This indicates that so-called norms of rationality are to a large part not real norms at all, but conceptual necessities. So is the "ought" or "must" in "if you believe P and Q, you must/ought to also believe P" like the "must" in "if it is true that P and Q, then it must also be true that P"? I think it's more like the "ought" in "if you go 'File' -> 'Save', the program ought to save the current document". Software can be buggy and fail to do what it's supposed to do according to its design specification. It is inconceivable that a word processor generally doesn't do any of the things that characterize a word processor. But it is conceivable that it fails occasionally and under specific conditions. (Then perhaps what Dutch books arguments try to show is that if you don't obey the probability axioms, you do something -- viz. give different evaluations to the same states of affairs -- which, if you did the same thing on a large scale, would rob you of your status as an agent with beliefs and desires.)

A Quiz (about "or" in English and in philosophers' English)

Diamond implicature

If I say "", you would often take me to have asserted both "" and "". A quick internet search didn't come up with any useful literature on this, so I'd be grateful for pointers.

Two arguments against modeling probabilities by size of propositions

To my surprise, there are quite a few people here at ANU who believe that probabilities of various kinds can be modeled in terms of relative size of propositions: something has probability 1 if it is true in all (or 100%) of the relevant worlds, probability 0 if it is true in none (or 0%), and probability 0.5 if it is true in half of the worlds (or 50%). I also find it surprisingly hard to explain why I think that's wrong. Here are two arguments I've come up with so far (apart from obvious worries about making sense of these fractions in infinite and proper-class cases).

Nomological possibility, chancy laws and zero-fit

Let's say that something X is nomologically possible if it is true at some world where the actual laws of nature are true. The actual laws may or may not be laws at this world. All we require is that they are true there.

Now consider a chancy law according to which a coin tossed in some standard way has a 50 percent chance of landing heads. For this to be a law at some world w means that it is part of the best theory of w, or that it represents the actual propensities in w, or something like that. What does it mean for it to be merely true at a world?

How to password protect certain features on a page with .htaccess

Here's an .htaccess trick I often find handy, but have never seen mentioned elsewhere, so I thought I might share. It gives you two routes to accessing the same files: one password protected and the other unprotected. In the files, you can then check how they have been accessed and turn on/off features accordingly.

RewriteEngine On
RewriteRule ^admin$ %{REQUEST_URI}/ [R,L]
RewriteRule ^admin/(.*) $1 [QSA,E=ADMIN:%{REMOTE_USER}]

AuthName "Admin"
AuthUserFile /full_path/.htpasswd
AuthType Basic
Allow From All
<Files admin>
require valid-user
</Files>

If you put this in your root dir (for example), you can now access all files either via /filename or, password protected, via /admin/filename (even though there isn't really an 'admin' directory on the server). In the second case, the server environment variable REDIRECT_ADMIN will store the username used to log in. So now you can do stuff like this in any file:

<?php
$admin = strpos($_SERVER['REQUEST_URI'], 'admin') ? $_SERVER['REDIRECT_ADMIN'] : '';
...
if ($admin) {
   print '<script src="ajaxy_admin_functions.js" type="text/javascript"><script>';
}
?>
<foo>
bar <?=($admin ? "<a href='?delete=765'>delete this<a>" : "")?>
</foo>
<?php
if ($admin && $_GET['delete']) {
   // process request
}
?>