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Comment by HPsquared | Hacker News Reader

The "slippery slope" principle applies here though: N+1 enables N+2, which enables N+3 and so on.

Slippery slope is a fallacy, not a principle. Just because you took N steps, that doesn't necessarily mean you will take N+1 steps.

It's a convincing fallacy because sometimes you do take N+1 steps. But just like in the article, heuristics aren't always right.

Slippery slope arguments aren't inherently fallacious. If you can justify one more climb on the grounds that probability of injury or death is very low then you will be able to justify every subsequent climb on the same basis.

Slippery slope arguments are inherently fallacies. They don't prove that something will happen.

Just because you can justify the next climb on the same basis, that doesn't mean you will. You could decide that you've already tested the odds one too many times.

"You could decide that you've already tested the odds one too many times" was the original point. Someone responded that the N previous times don't matter and N + 1 has barely any risk. Another poster countered that that argument as stated applies not just for N + 1 but for (N + 1) + 1 etc and therefore the slippery slope principle applies.

Of course if you add in "you could decide that you've already tested the odds one too many times" then it's a fallacy to invoke slippery slope because an off-ramp is explicitly specified. In this case slippery slope was mentioned only because N was dismissed as irrelevant.

Don't get on that greased sliding board that ends at the top of a cliff. Once you start sliding, it will be hard to stop because of the grease, and then once you slide off then end you will fall and die.

Do you really think this slippery slope argument is a fallacy? FWIW, wikipedia acknowledges slippery slope can be a legit argument when the slope, and it's chain of consequences, are actually real. https://en.m.wikipedia.org/wiki/Slippery_slope . Indeed, this is the very basis of mathematical induction.

From your linked article:

> The fallacious sense of "slippery slope" is often used synonymously with continuum fallacy, in that it ignores the possibility of middle ground and assumes a discrete transition from category A to category B. In this sense, it constitutes an informal fallacy.

"If you take N steps, you will take N+1 steps" is a fallacy whenever it's possible that you won't take N+1 steps.

Not what was said. What was said: if you DON'T take the Nth step, you then WON'T take the N+1 step.

"Not A -> Not B" is different logic than "A -> B". A is necessary but not sufficient for B.

>If you can justify one more …

Reminds me of Terry Pratchett quote "No excuses. No excuses at all. Once you had a good excuse, you opened the door to bad excuses.”

Full quote is fifth here: <https://www.goodreads.com/work/quotes/819104-thud>

When accounting for human psychology it does have validity: doing an enjoyable activity "one more time" has a risk of a habit forming, which has a non-zero probability. It is indeed possible.

The argument can certainly be used in a fallacious manner (e.g. by greatly exaggerating the probability of the further steps, saying they are inevitable if the first step is taken, etc.). It's logically valid to say that the first step enables subsequent steps to be taken.

Edit: I'd say that the slippery slope is perfectly valid rule of thumb in a lot of 'adversarial' situations. Once one side makes an error or fails somehow, the balance between the two sides can be disrupted leading to one 'side' gaining momentum. Just as between people, a similar 'adversarial' process can occur within the minds of individuals: between two ideas or patterns of thought/behaviour, one idea can gain momentum after a decision has been reached. Precedence is a strong force.

Like all fallacies, it's only a fallacy when it's fallacious.

Otherwise, it's just a regular d argument.

Maybe fallacies could be renamed "logical hazards" or something like that. Arguments that are at high risk of being false and require extra care, but not automatically false.

A pet peeve of mine is that the slippery slope fallacy can be defined as "modus ponens but wrong".

A fallacy should be a incorrect shape of an argument, a incorrect reasoning, not just a false statement.

but the risk is independent. so once you do the N+1 time safely, you are back to N and your next time is _also_ just an N+1.

Continuing to do something regularly doesn't ever mean you're just going to do it once more.

Psychologically, behaving in a certain way makes it more likely that you'll behave in the same way in the future. That's an integral idea underpinning justice systems.

True but it would be incorrect to assume that you can safely keep basejumping every day in a year, just because you haven’t died in the last 50 days. Eventually the stats say you will be 87% likely to have an accident when you consider your choice at the beginning of the year. It might be day 20 or day 300, but you won’t know what case you end up in. The chance of your next jump being your last is always the same, but that doesn’t decrease the risk of repeated trials.

Not exactly. If you've done it 50 days without an accident, your current chances of the accident happening in the remainder of the year are NOW less than 87%.

If you've made it Jan 1 to July 1 months without an accident, the chances of you making it to Dec 31 are now better than they were on Jan 1 -- because now they are just the chances of you making it six months, not a year.

The chances of flipping 6 heads in a row are 1/64. But if I've already flipped 3 in a row... the chances of flipping three _more_ heads in a row is 1/8, the same as always for flipping 3 heads in a row. The ones that already happened don't effect your future chances.

I meant to say starting a new year after the 50 past days, I see that wasn’t clear though.

Risk is independent of prior events, habits are not - I think that was what the anthropologist story is about

The risk is independent but the marginal enjoyment isn't. You don't get double the satisfaction from climbing twice as much.

Yes, but when you make a plan to find an acceptable cumulative future risk, planning to do it once a week for the rest of your life is planning to expose yourself to significantly more risk than doing it twice a year for the rest of your life.

You might still die in one of the next 20 instances. But you've added a lot more not-dead time in between them!

Saying "I can do one more with minimal added risk" every single time after not dying is true and yet pointless, because it's not a given that "minimal added risk" = "not dying." It's survivorship bias to not think frequency doesn't affect the cumulative odds of your future planning solely because you've already done a lot of trials.

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