I was having a discussion with some friends about Charlottesville, (BTW We're from and live in Ireland) My friend was supporting the idea of physically assaulting Neo Nazi's.

My argument was number that you shouldn't physically assault anyone based on their beliefs, no matter how terrible you think they are. His reply was 'but there Nazis'.

I responded if it's ok to attack Nazis, then who defines 'Nazis' ? If we give people pass on attacking Nazis then its my belief the term may be applied to people who are not Nazis but who just have a different ideology.

It was at this point another someone else jumped in and said 'that's a fallacy', to which I replied how, 'If I demonstrate a non-Nazi being called a Nazi, the logic of my argument holds'.

He was insistent I was using a slippery slope fallacy. We argued back and forth, ending in my asking him to demonstrate where the logical inconsistency of my argument is. To which he replied that it's called a slippery slope FALLACY.

I'd appreciate some clarification on weather or not I was using fallacy, I don't believe I was, as I've seen people saying its ok to punch Neo Nazi's and Ive also seen people who were non nazi being called nazi's. (i.e Trump supporters being called nazi's)

  • 1
    I think you employed the slippery slope fallacy and "moving the goalposts" fallacy. Your friend said "OK to attack Neo Nazis". Your counter "Not OK to call people Neo Nazis and then attack them". You assumed "Neo Nazi" is defined by the attacker, but that's not how words are defined. Changing the definition of Neo Nazi to suit your point was a logical fallacy (in my opinion), sorry.
    – user935
    Sep 2, 2017 at 2:03

4 Answers 4


I am not in favor of vigilante violence against any political position, but, although your position is likely to be correct, your argument for it is not valid.

It is the slippery slope fallacy to say if you allow X at some level of Y, then X is going to be possible at a different, unrelated level of Y.

Violence that does not kill is not killing, so saying that to permit slapping your partner for embarrassing you in public facilitates murder is obviously not a well-founded argument. One might die from a slap, but that is not likely. I could make such a major miscalculation that I slap you hard enough you have a heart attack from shock and die. But making the call to slap you is still not my deciding to kill. To render those equally immoral is misplaced.

"Well, who would define that level of Y?" does not dispel the basic fallacy either. People do just define things. There can be measures in a moral theory that simply appeal to convention or human intuition. We can set a standard and allow for a reasonable level of misunderstanding and ambiguity so that we know using that standard is generally safe.

Consider the Aryans on which 'The Order' in the play God's Country are based. They propose a 'point system' that logically implies that to be a man in their society if there are any Black people left in this hemisphere, one must eventually kill one. And although its is a fictionalized amalgam, these rules did in fact actually exist for some Skinheads in the U.S. in the 1970's and 80's.

Using physical violence against people who have openly sworn to kill is not necessarily a problem. If you capture them via violent intervention and deliver them to the police, you may be stopping them from killing. And if they are just being rhetorical and do not intend to kill, you would be dissuading them from targeted terrorist manipulation. If that is part of your definition of what Nazis have to do to be Nazis, it is a safe one to use in this circumstance. No?

A label is not a criterion. So what someone is called is not part of a moral deduction. People lie, especially about their enemies, and especially when using hyperbolic labels. But what they are doing or have done, are saying or have said can be used as valid criteria to decide how to treat them.

These people probably can't really choose a definition of Nazi that works and applies to Charlottesville. But if they could, they may well be able to support their position in some way. Your dismissal of all possible arguments they might make is highly likely to be right, but is still logically premature.

  • Just to clarify the scope of the discussion we were having, my friend was arguing that because they were nazis/white supremacists this in it's self was enough for him to allow or to not object to violence being used. There was no imminent or threat of violence.
    – Deepwinter
    Sep 1, 2017 at 19:02
  • OK, but that does not matter, because your defense did not involve a specific definition either. The entire defense was about the potential spreading of the label beyond the intended definition, which is a slippery-slope fallacy. The point is that there are definitions for which he could construct a defense (I just chose the one least fair to you on purpose, to make my point more easily) and without actually interrogating the weakness of his definition, or challenging him to pin it down, you are giving an argument that you think handles every possible one.
    – user9166
    Sep 1, 2017 at 20:25
  • 'Validity' is a stronger standard than just making sense and some fallacies still make a good deal of sense, but they are not philosophically valid, and trust in them has to be substantially tempered.
    – user9166
    Sep 1, 2017 at 20:29

"The Slippery Slope" is not necessarily a fallacy.

The technique is fallacious as when its only purpose is to scare the opponent when two categories are unrelated, but one of them is controversial. In typical examples, the argument is political, intended to force the speaker into positions that the speaker does not want to accept. The speaker abandons an argument rather than risk defending something that is unpopular or dangerous politically.

The Slippery Slope argument is legitimate when it is used to point out a distinction without an apparent difference:

-You oppose what Group A is doing, so you propose Policy 1.

-Policy 1 defines certain behavior and makes it illegal.

-But Group B does the same thing. Their activities would also become illegal (slippery slope!).

-You support what Group B is doing and you want the group to continue.

-Thus: the difference is arbitrary and has nothing to do with behavior.

Here, the speaker is simply offered the opportunity to explain .

  • There is no slope in your example, there is the denial of 'a level playing field' instead. That is its own unrelated problem, with its own customary name and framing. Your A and B are not at two different 'levels' of something, but are in fact comparable. For the metaphor of the slippery slope to mean something the slope must 'pull you downhill', there has to be a 'down' involved.
    – user9166
    Sep 1, 2017 at 6:49
  • I don't disagree that there is a context where the 'slippery slope' is used as a productive metaphor, rather than a fallacy, but this is just not an example of its use either way. For example, 'race to the bottom' arguments about the degradation of standards, like grade inflation, creation of dependency or defining deviancy down, use the metaphor but are not instances of the fallacy.
    – user9166
    Sep 1, 2017 at 6:56
  • jobermark. I think of the slippery slope as present in any example where a principle might have unintended and negative consequences if applied uniformly. Sep 2, 2017 at 0:25
  • You can think whatever you want, the metaphor requires a slope.
    – user9166
    Sep 2, 2017 at 1:12
  • jobermark. The idea of a negative outcome is the image of downward movement along a slope. Sep 2, 2017 at 3:11

Let's formalise, so we are clear what exactly we are talking about.


The basic structure of the argument is rather simple: if we allow A, B will necessarily or very likely follow (for A and B we can fill in certain acts or practices like euthanasia); B is morally not acceptable; therefore, we must not allow A either. Sometimes a further requirement is added: that A is in itself morally neutral or even justifiable. This does not seem to me a useful qualification: often the question is precisely whether A is justifiable, because the proposed principles that seem to justify A would justify B as well, and might therefore not be sound after all.

Usually two different versions of the argument are distinguished: the logical (or conceptual) version and the empirical (or psychological) version. The logical form of the argument holds that we are logically committed to allow B once we have allowed A. The empirical form tells us that the effect of accepting A will be that, as a result of psychological and social processes, we sooner or later will accept B. Inez de Beaufort distinguishes a third version which is philosophically uninteresting: the apocalyptical slippery slope. A horrible situation is sketched, which of course nobody would want but which is so highly speculative that the cogency of the argument-insofar as it exists depends more upon the horror than upon the likelihood. This seems to be the (rhetorical) version most frequently used in political debate. The history of the Nazis offers many highly demagogic but unsound references for this "Doomsday Argument," as Stich has called it. (Wibren van der Burg, 'The Slippery Slope Argument', Ethics, Vol. 102, No. 1 (Oct., 1991), pp. 42-3.)


There you have it, Nazis and all. It seems to be the empirical or psychological version of the slippery slope argument that you are concerned with. But in neither version, logical or empirical, is a fallacy involved.

In the logical version if A logically does entail B, there is not and cannot be a fallacy, an error of reasoning. In the empirical version, we are dealing with probabilities : it is a question of probability whether acceptance of A will lead to acceptance of B, not as a matter of logic but as a matter of fact. If we allow voluntary euthanasia, will we as a matter of fact be led psychologically to accept compulsory euthanasia, for instance.

I think the empirical slippery slope argument is actually on your side here. If we allow violence against Nazis, we are quite likely to be led psychologically to accept violence against Nazi-like groups - and who decides what amounts to being 'Nazi-like' ? And if the Nazis and Nazi-like can (properly) have violence used on them, then any group that seems as morally monstrous as the Nazis are likely to have violence extended to them, too, with the agents of violence deciding who is morally monstrous and how monstrous they are. Hold your ground !


Something could be a slippery slope, but it is not always fallacious. It is only fallacious if it is said that the first action will lead to something that is unrelated or absurd.

A good use of the slippery slope is if a child wants to stay up longer just for 30 minutes longer one night but you say if I let you do that tonight, it will be 30 more minutes the next night. This is a slippery slope but here it is reasonable to assume that the extra 30 minutes could lead to more in the next nights.

To go to your example, I would say it was a valid use since Neo-Nazi is a general label that has definitions that are not clearly set, so it is reasonable that anyone can apply it to anyone as Neo-Nazi can just be redefined.

Edit - Additionally, the argument they made needs to be made more clear and specific as their argument is essentially, "Nazis are bad so violence is fine," without actually giving good guidelines for when they think physical violence could be acceptable. If they say something specific like, "but there are people who advocate for ethnic cleansing," then you can further discuss if those beliefs can make it acceptable to take physical action.

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