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Closely related to the No True Scotsman fallacy is Sliding Definition Ploy1. It goes like this: "for the sake of argument", give a slightly-odd definition to some common term, like Mind, or Freedom, or Justice, or Beauty. Deduce some consequences from that definition (ideally, this stage should take a while, to overflow your audience's input buffers). Claim that these deductions tell you something about the ordinary meaning of the term you started with. Better yet, don't claim it; just proceed as if they do.
SDP is, unfortunately, endemic to philosophy, or at least was when I last took a look. In philosophy, one of the big problems is that all the really interesting ideas you want to talk about (Truth, Justice, Ethics, Vision, Desire, the Soul, Mind, Body, even simple things like "looking"2) are ill-defined. The other big problem, of course, is that you can't do experiments on most of these things (even if you're the sort of philosopher who believes we can trust our senses and the sort who's prepared to accept the validity of the scientific method, which is by no means all of them). So you're left with pure reasoning. Mathematicians can get away with relying on pure reasoning, because they're working with abstract things that are precisely defined. Sorta3. So, in order to get any traction at all on their problems, philosophers often have to provide definitions of common terms. This allows the unscrupulous philosophers4 to insert a Sliding Definition Ploy or two.
SDP is also common in arguments about politics: we're all in favour of Liberty, Justice, etc, but these terms are all ill-defined, and by choosing definitions carefully, it's easy to show that your opponent is opposed to any given Good Thing.![[livejournal.com profile]](https://www.dreamwidth.org/img/external/lj-userinfo.gif)
zompist has written more about this in one of his rants, in which he also elaborates on the linguistic problems with definitions.
There are lots more standard logical fallacies: Wikipedia has a list (Googling will reveal several others), and here's infidels.org's guide to logic and fallacies, which also has what looks like a good section on what logic is, what it isn't, and what it's useful for.
[By the way, I am no longer eating salted porridge. I am now about to tuck into a sausage sandwich. An organic venison sausage sandwich, no less, filled with sausages from the farmers' market at Queen's Park yesterday :-) ]
1 The term is due to John Puddefoot, AFAIK.
2 I know a philosopher who recently wrote a paper on the difference between "looking" and "watching". Or possibly "watching" and "seeing". Or something like that. It's subtle stuff.
3 At the risk of being accused of SDP myself, this is probably the best definition of mathematics we have.
4 A depressingly large subset, from what I can see.
SDP is, unfortunately, endemic to philosophy, or at least was when I last took a look. In philosophy, one of the big problems is that all the really interesting ideas you want to talk about (Truth, Justice, Ethics, Vision, Desire, the Soul, Mind, Body, even simple things like "looking"2) are ill-defined. The other big problem, of course, is that you can't do experiments on most of these things (even if you're the sort of philosopher who believes we can trust our senses and the sort who's prepared to accept the validity of the scientific method, which is by no means all of them). So you're left with pure reasoning. Mathematicians can get away with relying on pure reasoning, because they're working with abstract things that are precisely defined. Sorta3. So, in order to get any traction at all on their problems, philosophers often have to provide definitions of common terms. This allows the unscrupulous philosophers4 to insert a Sliding Definition Ploy or two.
SDP is also common in arguments about politics: we're all in favour of Liberty, Justice, etc, but these terms are all ill-defined, and by choosing definitions carefully, it's easy to show that your opponent is opposed to any given Good Thing.
zompist has written more about this in one of his rants, in which he also elaborates on the linguistic problems with definitions.There are lots more standard logical fallacies: Wikipedia has a list (Googling will reveal several others), and here's infidels.org's guide to logic and fallacies, which also has what looks like a good section on what logic is, what it isn't, and what it's useful for.
[By the way, I am no longer eating salted porridge. I am now about to tuck into a sausage sandwich. An organic venison sausage sandwich, no less, filled with sausages from the farmers' market at Queen's Park yesterday :-) ]
1 The term is due to John Puddefoot, AFAIK.
2 I know a philosopher who recently wrote a paper on the difference between "looking" and "watching". Or possibly "watching" and "seeing". Or something like that. It's subtle stuff.
3 At the risk of being accused of SDP myself, this is probably the best definition of mathematics we have.
4 A depressingly large subset, from what I can see.
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