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PaperclipPerfector  5mo ago (text post)   4462 thread views

Small-Scale Question Sunday for June 16, 2024

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Can somebody explain to me in simple, preferably monosyllabic words: what does the expression One man's modus ponens is another man's modus tollens mean?

An example of this kind of misunderstanding happening is Robin Hanson on sexual redistribution. Hanson compares arguments for redistribution of sexual status & redistribution of wealth but notes the same people rarely are for both policies.

Libby Libertarian, a stout free-marketist, thinks Hanson is saying "sexual redistribution is bad."

Sally the Socialist, who lives in a commune, thinks Hanson is saying "sexual redistribution is good."

As other commenters have explained: A logical argument usually has two ways to take it.

I would reframe it thus; Libby the Libertarian makes the argument that income redistribution is morally equivalent to sexual redistribution. In both cases, the state is forcibly taking something from those who have it and giving it to people who claim to need it. Libby is making this argument because she is against income redistribution and is appealing to the shared intuition she thinks we all share that sexual redistribution is morally monstrous to convince us that income redistribution is evil as well. That if sexual redistribution is rape, then taxation is theft and welfare is slavery.

However, along comes Ike the Incel, who reads her argument, and agrees that income redistribution and sexual redistribution are isomorphic, but bites the other bullet. If it is morally justified for the government to take a bit from those who have more than enough to help the less fortunate when it comes to dollars, why is not morally justified to do the same when it comes to sex? The capitalist bourgeoisie would not have their wealth but that society provides them with free schooling and roads and property enforcement, so it is appropriate to ask them to chip in to keep society going. Likewise, women would not be able to stop men from having sex with them without police to stop rapes and food stamps to stop them from resorting to prostitution, so it is morally justified to ask them to give back by providing sex to the sexless and breeding the next generation. Hence, government mandated girlfriends.

At this point Ike has taken Libby's argument and reversed it from Modus Tollens into Modus Ponens.

Libby:

  1. If income redistribution is justified, sex redistribution is justified.
  2. Sex redistribution is not justified.
  3. Therefore, income redistribution is not justified.

Ike:

  1. If income redistribution is justified, sex redistribution is justified.
  2. Income redistribution is justified.
  3. Therefore, sexual redistribution is justified.

So that when Libby asks Ike if he is in okay with the government forcing women to have sex with men, given that he is okay with the government stealing from people and forcing them to work without pay, Ike puts on his most manly, chiseled face, and replies "YES".

I think you're right, and I guess that means, technically, one of Libby or Sally is making fallacy of the converse.

It is an easy mistake for me to make since Hanson's formulation appears to be symmetrical (biconditional statement)

If we have a phrase:

If A, then B.

From this, one can say, A, hence B.

But some might say not B, hence not A.

This says that, if you make a claim, some might choose not to go with the proof you meant, but choose to say that the first phrase must be false.

Now I will stop with the use of short words.

Okay, more clearly.

In general, when you have arguments, there are assumptions. You can make some argument, and reach the conclusion, and so claim that that the conclusion must be true, this being a form of modus ponens ("the putting way"). But people could instead think the conclusions are obviously false, and so conclude that a premise must have been wrong, which is modus tollens ("the overturning way"). This is pretty much always going to be possible in arguments.

It's a brief way to point out that arguments must be taken to their logical conclusion in order to be properly considered, and people who refuse to "bite the bullet" and address the full implications of the positions that they espouse are either stupid or lying. Below are some examples found with Google.

Example

Premise: All human life is equally valuable.

Observation: I can point to a human life that has approximately zero value.

Conclusion: Either all human life has approximately zero value, or all human life is not necessarily equally valuable. Anybody who tries to take a third position on this issue is either stupid or lying.

Example

Premise: Permanently damaging a healthy human body in order to alleviate a mental condition is bad.

Observation: Sex-change/gender-affirmation surgery involves permanently damaging a healthy human body in order to alleviate a mental condition.

Conclusion: Either sex-change surgery is bad, or pemanently damaging a healthy human body in order to alleviate a mental condition is not necessarily bad. Anybody who tries to take a third position on this issue is either stupid or lying.

The terms “modus ponens” and “modus tollens” come from formal logic. They tell you how to deduce conclusions from statements.

Modus ponens says that if you know that A is true, and that B is true whenever A is true, then you can deduce that B is true. For instance: “If someone is a hunan, then he is mortal. Socrates is a human. Therefore, he is mortal.”

Conversely, modus tollens says that if you know that B is true whenever A is true, and you know that B is not true, then A is not true. “If someone is a human, then he is mortal. Zeus is immortal. Therefore, Zeus is not a human.”

The full expression extends these terms to the realm of politics and morality. For a naive culture war adjacent example: “Christianity says that gay sex is bad. Christianity is good. Therefore, gay sex is bad.” This is a sort of moral equivalent to modus ponens as described above. But, if you support gay rights, then you can do this in reverse: “Christianity says that gay sex is bad. Gay sex is good. Therefore, Christianity is bad.” This id the equivalent of modus tollens.

The expression thus can be viewed as saying “if you support a consequence because a preexisting belief of yours says that it’s good, then someone else could just as easily reject that consequence and say that your preexisting belief is bad.”

Let's say you have a statement:

If A, then B.

There are two syllogisms that can be derived from this statement, one of which is referred to as Modus Ponens and the other of which is Modus Tollens.

Modus Ponens:

  1. If A, then B
  2. A
  3. Therefore, B

Modus Tollens:

  1. If A, then B
  2. Not B
  3. Therefore, not A

Where the statement / joke comes in is when you start making an actual argument where the two people agree on the conditional, but one is arguing that A is true and the other is arguing that B is false. Let's say something like:

If morality is objective, there is a God.

The first person takes the objectivity of morality as proof that God exists, but the second person takes the non-existence of God as proof that morality can't be objective. Despite both parties accepting the conditional, they still believe different things.

Thanks, I think that's the best explanation of the three, if I understood it right. A mutually agreeable statement if A, then B can mean that either B is true, or A is false, depending on your other beliefs, right?

Right, so the expression comes from that fact -- the mutually agreed upon statement points in two directions. One person can say "Aha, so we know that B is true." and the other person can say "Aha, so we know that A is false."

I just made a connection after somebody linked here in the main thread. At least in some cases, this is actually just yes_chad.jpg in high register!

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