I'm not sure if this qualifies as a fallacy, but it is a form of deception that I've seen before.

Imagine a person who doesn't believe in heavenly bodies, other than stars and planets. So he says,

People who believe in black holes are likely to believe in other space oddities, too.

The implication is that there's nothing in space but stars and planets.

This isn't an example of a tautology but a ______. (I'm searching for the name of this particular propaganda technique.) Like I said I'm not sure if it qualifies as a fallacy, because it doesn't sound like an argument. On the other hand, it does sound similar to an ad hominem attack, or the poisoning the well variation.

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    It qualifies as a rhetorical flourish, "if you are buying X there is a bridge I have to sell you", a type of sarcasm by hyperbole. Like any other rhetorical device it can be used for legitimate or untoward purposes, and it can only serve ad hominem purposes (discrediting the opponent) when the sarcasm isn't overt. By the way, black holes are stars too. – Conifold Sep 2 '18 at 20:16
  • Technically, it's a statistically invalid conclusion because of the words "likely". To be correct, you'd have to poll a random sample of people who believe in black holes and see what percentage believe in other space oddities (you'd have to define "likely" as well). @Conifold is correct, and this could also be considered a faulty generalization ("people who shoplift are more likely to commit murder", "people who use marijuana are more likely to use hard drugs"). – user935 Sep 2 '18 at 20:49
  • OK, I could call it a rhetorical flourish, statistically invalid conclusion or faulty generalization. Got it. – David Blomstrom Sep 3 '18 at 4:04

Appeal to ridicule (reductio ad ridiculum)

Comparing belief in black holes to belief in 'other space oddities' (unspecified but presumably including highly improbable or even impossible things) is not a good argument. Logically it has no cogency. It is merely an appeal to ridicule, which counts as a fallacy on most reckonings. Compare : 'If you believe the Chinese economy will crash, you'll believe there are fairies at the bottom of the garden'. Laughter all round but no cogent argument for the inference.

The ridicule is made worse in this case because (1) 'space oddity' is a vague and unspecific term) and (2) there is no reason why a black hole should not be a 'space oddity' in some distinct respect and yet exist. After all in a black hole the normal rules for behaviour in space/time do not apply. A black hole is a singularity. That makes it a 'space oddity' in a distinct and scientifically respectable sense but counts for nothing as an argument against the existence of black holes.

To put the point another way ...

'Space oddity' is too imprecise a term to argue much over. There is a singularity about black holes &, because of this, for a considerable time many physicists did not believe in their existence. In this sense they are 'space oddities'. My point is that being a space oddity, if we have to use this term, is no argument against a black hole's existence. Believing in a black holes does not commit one to believing in the existence of the ether, 108 dimensions of space/ time, or the moon's being made of green cheese - other space oddities of the sort your ridiculer presumably has in mind.

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  • Well, your analogy is not really good, because the initial example assumes black holes are space oddities. While I see no connection in your analogy. – rus9384 Sep 3 '18 at 9:56
  • Response in revised answer. I await the reply, rejoinder, surrejoinder ... – Geoffrey Thomas Sep 3 '18 at 12:02
  • Interesting answer. At first, it didn't sound like a good fit, yet that's essentially what the person is doing - making it sound like people who believe in something are SO dumb they'll probably believe in something similar. – David Blomstrom Sep 3 '18 at 20:24
  • @David Blomstrom. Comment much appreciated. Your presence on PSE is very welcome to me - I follow your contributions. Best - Geoffrey – Geoffrey Thomas Sep 4 '18 at 9:00

Its an abuse of something true. There are many cases when accepting one truth forces you to accept another, or at least forces you to except that the opposite is false.

One such term used to describe this is Mutual Exclusivity

There is absolutely a logic train for beliefs that force you to accept another, but what you are describing is an abuse of this.

That person is committing a Causal Fallacy about your beliefs.

As far as describing it as an attack? Im not sure. Its some kind of a non sequitur straw man.

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    Interesting. I'm going to do some research on the terms you listed. – David Blomstrom Sep 5 '18 at 4:42

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