Before I begin it is important that I differentiate between Slippery Slope Arguments, and Slippery Slope Fallacies.
Slippery Slope Arguments are a form of inductive reasoning which notes that those who hold to a certain position (hitherto referred to as position A) either eventually come to hold a bad belief (hitherto referred to as position B), or their students/descendants come to hold that bad belief (i.e. position B), or it is reasoned that position A should logically lead to position B. It is then induced that there is some quality about position A which usually or necessarily causes a belief in position B. Since position B is bad, it then follows that position A is also bad (or at least too dangerous to be considered).
The Slippery Slope Fallacy actually takes exactly the same form as the Slippery Slope Argument. The only difference is that there lacks sufficient evidence to link position A to position B. Indeed, this is the problem with inductive reasoning in general, for the very nature of induction merely gives strong support for a conclusion, but it cannot demand it. Even the best Slippery Slope Arguments can only say that position A can/probably will/often will lead to position B. It cannot guarantee it. Once someone either starts saying that A guarantees B, or if one doesn't take the time to establish sufficient evidence for A leading to B, the Slippery Slope becomes a fallacy.
We need to be careful when someone makes a Slippery Slope argument because it is significantly easier to propose a Slippery Slope than it is to truly present one. In order to propose one, all you need to do is to show that A is come how closer to B than your own position. However, showing that Pennsylvania is closer to Florida than New York doesn't mean that I'll end up in Miami whenever I drive to Philadelphia. To demonstrate a Slippery Slope you have to actually show that there is a slope: a cause and effect, as well has sufficient history showing a correlation.
Slippery Slopes in Action
There are many Calvinists who love to project the Arminianism/Calvinism debate back onto the debate between Augustine and Pelagius in the late 4th century. When doing so, Calvinism clearly goes to the Augustinian side since it really is the Protestant version of what Augustine taught on these matters. However, one has to be either grossly ignorant or malevolently deceitful in order to claim that Arminianism is akin to Pelagius's views (Arminianism is in fact very similar to the Semiaugustinian view which arose in the early 5th century).
For those who are neither ignorant nor deceitful but still want to use the Augustine/Pelagius debate as a Calvinist claim to legitimacy, they resort to saying that Arminianism leads to Pelagian views. Usually, this claim is simply stated in such terms as "on its way to Pelagianism" or "it is the first step towards Pelagianism". What I have never heard is any attempt to explain how a belief in Arminianism would actually lead to a belief in Pelagianism, nor have I heard any examples of Arminians who eventually became Pelagians.
I would also add that I have only ever heard this particular argument from the most extreme Calvinists. Indeed, extremists will often use slippery slopes argumentation to justify why they are so extreme. This is why Slippery Slope arguments are usually specific examples of stronghold type rhetoric.
Mind you, Arminianism is closer to Pelagianism than Calvinism is. However, Arminianism is also closer to Calvinism than it is to Pelagianism. Does it make sense that any Semi-pelagian who comes to believe in Arminianism will eventually become a Calvinist? I doubt it. Like I said in the introduction, Showing that a position is between your position and a heresy does not prove that holding it will lead to that heresy. This is what happens when someone tries to understand topography while looking at a 1st grader's map. Location does not imply inclination.
Arminianism/Semiaugustinianism are indeed middle ground positions, but I have found it to be rare that a middle ground position leads to an extreme. Indeed, what I have usually found is that when one moves from one extreme to another, it is usually by way of a great leap over the middle ground positions. A Calvinist, who believes that they must believe in Calvinism or end up a Pelagain, is far more likely to become a Pelagian due to a sudden disbelief in Calvinism than a typical Arminian.
First, I need to explain what I mean by liberalism. By liberalism I mean theological liberalism, not political liberalism. Theological liberalism states that the Bible was written by humans, and as such it to be understood primarily as their opinions. We then have the right to judge whether or not their opinions are accurate, and do not have to judge our opinions by theirs. This is to be contrasted with conservative Christianity, which understands the Bible to be rule of faith by which we judge whether or not our opinions are on the right track.
Now many Calvinists have argued that Arminianism leads to liberalism. The primary evidence for this is that the Remonstrance church in Holland (which was started by Arminius's original followers) is incredibly liberal. Of course so is Geneva, but somehow that doesn't count...
Here is a video which makes this argument fairly well: "Arminianism: Root of Christian Liberalism?". Now, we can ignore the first part which is a vacuous argument from authority about Arminianism being Semi-pelagian (which consists of putting on happy imagination hats and pretending not only that the Dortians tried really really really hard to properly understand Arminius, but that this, in of itself, somehow makes them automatically right).
Though the conclusion of the argument here is false, what is interesting in this video is that it is an example of a Slippery Slope argument done properly. It gives historical evidence and give a reason as to why Arminianism would lead to liberalism. Now the historical evidence is faulty* and the reason given is based off of a series of false premises**, but the argument itself is presented well.
However, this example is more the exception than the rule. Usually, in my experience the argument is based off of many liberals believing in free will. Well, if Arminians believe in free will, and liberals believe in free will, then one leads to the other. However, even though most liberals today believe in free will, that wasn't always the case. And the only reason they do is because of existentialism, not because they used to be Arminian.
The biggest problem with this argument though is that it just doesn't correspond with history. Both Calvinist and Arminian churches went liberal because liberalism has nothing to do with sotierology. In fact, I wouldn't be surprised if the percentages were about the same.
The End Result
Slipperly Slope arguments are really a specific form of Stronghold rhetoric, which I have mentioned before. Like all Stronghold rhetoric, Slipperly Slope arguments expose why the arguer holds the stances that they hold.
However, Slipperly Slope arguments are themselves rather dangerous. Slipperly Slope argumentation excludes the middle ground as a serious position. As such, if someone were to lose faith in the "established position" they often leap straight to the bottom of the slope without seriously considering any alternatives.
Perhaps this isn't a fear for Calvinists due to their belief in eternal security, but it is something which bothers me. After all, I have to constantly watch former Calvinists leap right over classic conservative Arminianism straight into the very beliefs that they were trying to avoid. For me, there have just been too many innocents who have worked so hard avoiding a bit of a slope that they've driven right off the cliff.
* I've already said it a couple of times, but the history mentioned in this video is faulty because Calvinist denominations went just as liberal as Arminian ones. Indeed, I remember reading one Calvinist who said that belief that all which came to pass was by the hand of God is why he believed that he needed to head in the same trajectory of the surrounding culture (a.k.a being liberal).
** The poor premises are:
- One does not have to believe that God directly put words into the prophets' mouths in order to believe in the reliability and infallibility of Scripture.
- Most evangelicals start with a belief in infallibility and only then start to consider why. There are very few who hold to infallibility as a consequence of their other beliefs
- Even if one had to believe that God took over the will of the prophet in order for Scripture to be infallible, most Arminians (including myself) hold that God can and even has overtaken or changed the wills of humans before. We just hold that He generally doesn't, and that He doesn't when it comes to salvation itself.
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