Posts Tagged ‘logical fallacy’
There are lots of good books and websites (see: The Fallacy Files and Your Logical Fallacy Is ) on critical thinking, logic and fallacies, but unfortunately there’s still widespread ignorance of such things. So, I think it’s always a good idea to discuss common errors in reasoning with a view to explaining why they are errors.
The “Slippery Slope” is one of the most frequently misused and misunderstood argument forms — because those who employ it believe it to be a strong argument form when it is, in fact, the exact opposite. It’s a commonly used phrase and most who use it are attempting to show that if one does “A” then a chain of events will occur which will eventually lead to the undesirable result “D”, for example. The imagery is quite simple: by initiating “A” one has stepped out onto the top of a steeply angled and slippery incline, so one will slide from the top of the incline all the way to the bottom without being able to stop — and at the bottom lies the undesirable outcome (“D” in our example). Therefore, by initiating “A” one has really set a course for “D” because “A” leads to “D” and we can’t stop that journey once we’ve begun. So, the only way to avoid ending up at “D” is to not initiate “A.” Here’s a little graphic:
As we can see, “A” leads straight down the slope to “D” passing through the two intermediate points of “B” and “C” — we’ve slid right from the top to the bottom without being able to stop. This would be all well and good if the chance of going from “A” to “B” is 100% and the chance of going from “B” to “C” is 100% and from “C” to “D” is 100%. In short, if each link in the chain is a certainty. In that case we would have something known as a hypothetical syllogism or “chain argument” in logic. The reason for the name “chain argument” should be fairly obvious: each step (“A”, “B”, “C”, etc.) can be likened to a link in a chain and as long as each link is at 100% strength, then the chain itself will be at 100% strength. So, as long as each step is certain, then we can be certain that if we begin at “A” then it is certain we will end up at “D” — we can be certain of sliding right to the bottom of the slope.
Where the Slippery Slope quickly weakens is when there is not certainty that each link in the chain will occur — where there is only a probability that one or more links will follow on from the previous link. Let’s take a look at another graphic:
Here we have an example of a Slippery Slope where the transition from “B” to “C” gets a bit sticky and there is only a 70% chance that getting to “B” means proceeding on to “C.” See what that does to the final chance of arriving at “D” now? In the previous graphic each link was 100% certain, so we could go right from “A” to “D” knowing there was a 100% chance of getting to “D” from “A.” Now we can only be 70% certain that if we initiate “A” that it will result in “D.” That is, 3 times out of 10 doing “A” will not lead to “D” as a result. One might be tempted to think those are still pretty good odds, but that is simply one flaw in one link — let’s look at what happens when there are flaws in more than one link. Here’s another graphic:
We now have a situation where each link in the chain has only a 70% chance of leading to the next link — see what that has done to the chance of ending up at “D” now? The weaknesses are cumlative: meaning that each time there is less than certainty the diminished chance acts on the previously diminished chance quickly weakening the overall chance of ending up at the bottom of the slope. Now we have a situation where two thirds of the time we will not end up at the bottom of the slope — two thirds of the time “D” does not occur. Add in more links and the final chance will plummet further. This is a fairly simple example with only four links at quite a high probability of 70% — imagine what happens to an argument with six, ten, fifty or over one hundred links — a common characteristic of most slippery slope arguments is that the starting point is far removed from the undesirable end point.
The crucial point to understand is — Slippery Slope arguments are inherently weak arguments. When someone argues using a Slippery Slope they are using a very suspect methodology that should never be accepted at face value. One always needs to look at the number of potential links in the slope and the likeliness of each link occurring. Most times when someone is using a Slippery Slope argument they are attempting to dissuade the initiation of an action by arguing the inevitability of a resultant undesirable situation — they are generally not employing a hypothetical syllogism (“chain argument”) and therefore the outcome is not certain — only probable. That means that it’s very unlikely a given Slippery Slope situation will be inevitable — and if it is found to be, then it’s a hypothetical syllogism. Some may, indeed, prove to be highly likely — but a Slippery Slope always needs to be carefully examined.
Often times the arguer also ignores the fact that we can frequently choose to stop our slide down the slope by exercising our will to choose as individuals and societies — we can set limits to certain actions in law and by social convention. The arguer’s aim is to present a situation where real choice is taken out of the equation in order to simplify the argument down to a forced binary choice of initiating “A” or not initiating “A.” By presenting the argument as if there is no real choice, no braking point on the slope, the arguer seeks to strengthen the overall argument by forcing a false dichotomy — an artificially limited choice between the two alternatives of: “A” which means not avoiding “D” or “Not A” which means avoiding “D.“ In the vast majority of cases, the situation is much more subtle and nuanced — and when someone argues in such a way to grossly simplify the situation you should be wary that it is because complexity, nuance and careful consideration hurts his or her case. In short, the arguer is pulling a fast one in order to hide inadequacies in the overall argument.
So, next time someone says something like, “But that would put us on a slippery slope to…” understand it’s probably quite unlikely and almost definitely not a certainty. At the very least, when you hear the phrase you should be aware that a careful examination of the case is immediately warranted.
EXAMPLE: Interestingly, just hours after I posted this there was a good example on UK Channel 4 News of an appeal to a Slippery Slope in a piece discussing gun control in the US in the wake of the Aurora shootings (at 2:55):
The arguer states that, “it [gun control] is a Slippery Slope once you start down that path taking away our freedoms.” Imagine how many intermediate steps there could conceivably be between initiating some form of stricter gun control (e.g. simply banning large magazines as is suggested in the video) and the end point of “taking away our freedoms” — then consider the example above with only four stages in the slope and how quickly it weakens. The arguer attempts to end the discussion before it starts by making it seem that if we take even the tiniest measure of gun control, then the state will end up “taking away freedoms” wholesale. He also ignores the fact that society can choose to draw the line where it wishes (put the brakes on at any point on the slope) and, for example, control the availability of weaponry but not remove rights to free speech, assembly, etc. Or, simply control the availability of certain types of weaponry and ammunition without banning all weapons outright.