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Recently I was talking to a friend of mine, a vegan. Here's what she said: "I was talking to a vegan philosopher once, and he said that he is a vegan because there is no good argument against veganism". Now, my question is not about veganism in particular, but about the type of argument the philosopher used, which has the form:

There is no good argument against position X, therefore I believe that X is right.

But something tells me that this type of reasoning is fallacious. What the utterer really means is this:

No one has yet come up with a good argument agaist position X, therefore I believe that X is right.

Now, the problem becomes apparent: the fact that no one has ever come up with a good argument against position X does not guarantee that there really is none. It seems to me that the argument is inherently inductive.

Is this just really good old inductive reasoning in disguise? Also, let's suppose that by a "good argument" the philosopher really meant a valid and sound one.

  • Sounds like Russel's teapot waiting to happen. en.wikipedia.org/wiki/Russell%27s_teapot The argument from ignorance is not an induction. A long succession of things not happening is not an inductive basis, and does not mean anything. There will be a day the sun does not set. – jobermark Apr 8 '16 at 18:24
  • This question is similar to What fallacy dismisses a conclusion because supporters give invalid arguments for it? philosophy.stackexchange.com/questions/32257/… The answer is yes, the fallacy is called ad ignorantiam, appeal to ignorance, and the standard rebuttal is "the absence of evidence [argument] is not the evidence of [argument for] absence". – Conifold Apr 8 '16 at 22:24
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Yes, "no argument against X, therefore X" is the fallacy named Argument from ignorance.

A related statement is "the absence of evidence is not the evidence of absence", here applied with "evidence = evidence of a counterargument".

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I agree with you that the argument is inherently inductive. But in modern parlance that may be as good as it gets.

The argument is rhetorically neat. It makes you think. It precludes many obvious arguments against. And it packs in a number of valid or viable assumptions.

The assumptions are: First, there may be some good arguments for being a vegan. Second, most people have not critically considered these arguments, and have adopted the anti-vegan position dogmatically or out of habit. Third, there are no positive immutable truths either way. Fourth, the vegan argument, once critically adopted, stands as long as it is not falsified, in Popper's famous formulation.

Again, the argument is not a proof of any sort. It is sophistic, ironic, and rhetorical. But compelling in a world devoid of absolute truths. It reverses the burden of proof and confronts the unexamined assumptions of the carefree meat swallower.

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There are a couple issues with arguing in this manner:

  1. "(Many people think) meat is delicious." That is a debatable reason against veganism, but it is a reason. The "vegan philosopher" saying there are no "good" arguments against veganism is potentially (although not necessarily) begging the question - dismissing arguments that are logical because they disagree with a preconceived notion that he is trying to justify in the first place.

  2. There very well might be good arguments against something, but one may not know them out of ignorance of the matter.

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To answer your question you firstly have to set the "refutation argument" criteria. The trick here is that it might not be possible at all. All this reminds me of Popper criteria for scientific theory - e.g. the one that actually be refuted. So you have to ask your friend a question what in his view be the kind argument which he will accept as valid contra-veganism argument. When this will be set clear it would be much easier for you find one. And if your friend do not provide such objective criteria then the theory cannot be proven just as it cannot be refuted --> the argument itself is futile.

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Jo's named fallacy is a good response (Argument from ignorance). However, such an argument is also made as part of abduction, which is a cognative process similar to deduction and induction. In abduction, you assume the most likely hypothesis to be true. In some situations, the lack of any argument against the hypothesis may be construed as making it "most likely," so one might use abductive reasoning there.

Abduction is a tricky concept in philosophical literature. It is not fully accepted as "valid" rational thought, and yet everybody does it. In fact, the step going from "the last 1,000 apples fell from the tree with an acceleration of 9.2m/s^2" to accepting "what goes up must come down" as a universal truth is abduction. Science has no way to positively confirm a theory, only ways to falsify it, so if you ever use science in the positive direction, you have actually engaged in abduction at some level (scientists would argue it to be a highly justified case of abduction).

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