Wolfgang Schwarz

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
}
?>

Desiring to undo one's existence

Sometimes I wish I hadn't done something, and that I could undo what I did. That is a coherent desire. What I desire is after all not that the world be such that at time t1, I do X, and then at t2, I do something else to the effect that at t1, I didn't do X. That's nonsense (unless I wish to inhabit a branching universe, which, let's stipulate, I don't). Rather, I desire that at t2, I do something to the effect that at t1, I didn't do X in the first place.

A harder case: suppose I wish I had never existed, and wish to undo my existence. That still makes sense, I guess. It's like the wish to be somebody else: I wish to do be a person who does something such that by doing this, they make it the case that the person I in fact am never came into existence.

Conceivably possible zombies

Does the conceivability of zombies threaten type-A materialism, the claim that all mental truths are a priori entailed by the physical truths?

We can imagine beings exactly like us in all physical respects, but lacking consciousness. But this doesn't threaten type-A materialism (as I mentioned here). After all, it isn't a priori that materialism is true. It could have turned out that ectoplasmic states, rather than brain states, occupy the causal roles that, by analytic necessity, belong to mental states. Suppose it turned out that way. Then duplicating only our physical constitution would result in a being that is physically just like us, but lacking consciousness. So by type-A materialist lights, it is conceivable that things are such that there are beings physically just like us without consciousness.

Laws, necessities and properties: some old views, some new ones, and some arguments

Is it metaphysically necessary that like charges repel? One might think so: one might think that "charge" is partly defined by its theoretical role, so that this claim comes out analytic. Or one might think that science reveals to us the essence of properties, and that it is part of this essence of charge that like charges repel.

If that law about charges is metaphysically necessary, one might suspect that quite generally, nomological necessity coincides with metaphysical necessity (though see below for an argument against this suspicion):

Are all truths entailed by logical truths?

Sorry, the server has been down quite a lot recently. Hope it's back to normal now.

Here's the talk I gave at Kioloa. It's partly identical to the talk I gave at GAP.6 in Berlin, but with more speculative ideas towards the end and less missionary appeals in between.

Are all truths entailed by logical truths? Depends on what we mean by "all truths" and "entailed" and "logical".

Let's understand a truth to be a true sentence of English, possibly enriched by logical vocabulary. As for entailment, let's distinguish metaphysical entailment (necessarily, if P then Q) from analytical (or conceptual or a priori) entailment. The precise definition of these notions, and the differences between them, won't matter.