If I use the IBE argument to justify my belief in the existence of other minds, but I don't know how the argument reached its conclusion, can I just trust the experts who formulated the argument or will it be circular reasoning?
If I rely on my common sense and believe in the existence of other minds, but I do not know whether the beliefs of common sense are justified, can I rely on experts who say that we can trust common sense, or will it be circular reasoning?
In the Heideggerian œuvre other minds are included from the start in Dasein's primary mode of Mitsein (being-with). E.g. from Being & Time (116):
[The] positive Interpretation of Dasein which we have so far given, already forbids us to start with the formal givenness of the "I", if our purpose is to answer the question of the "who" in a way which is phenomenally adequate. In clarifying Being-in-the-world we have shown that a bare subject without a world never 'is' proximally, nor is it ever given. And so in the end an isolated "I" without Others is just as far from being proximally given. If, however, 'the Others' already are there with us [mit da sind] in Being-in-the-world, and if this is ascertained phenomenally, even this should not mislead us into supposing that the ontological structure of what is thus 'given' is obvious, requiring no investigation. Our task is to make visible phenomenally the species to which this Dasein-with in closest everydayness belongs, and to Interpret it in a way which is ontologically appropriate.
To quote the IEP:
[The phenomenal reduction] enables the phenomenologist to go “back to the ‘things themselves'”(Husserl 2001, 168), meaning back to the ways that things are actually given in experience. Indeed, it is precisely here, in the realm of phenomena, that Husserl believes we will find that indubitable evidence that will ultimately serve as the foundation for every scientific discipline. As such, it is vital that we are able to look beyond the prejudices of common sense realism, and accept things as actually given.
Hence the phenomenological starting point is direct experience which is culturally embedded from its earliest development.
OK let's take some branching possibilities. We meet someone, call them nibroc, who we ask if they are a p zombie. There are a few different scenarios that may be occurring
- nibroc is not a zombie
- nibroc is a zombie and is an authority on that
- nibroc is a zombie but is not an authority on that but some people are
- nibroc is a zombie but is not an authority on that and no-one is
1 means we should not be solipsists. 2 means not all appeal to authority on solipsism assumes other minds^. 3 repeats 1 and 2 for others like nibroc. 4 is the only option: but how can you decide that no-one is an authority without just assuming that no-one is?
Anyway, there are reasons (ones which are not obviously question begging) to suppose such an authority can exist. The bible is oft said to be an authority on morality; it does not have a mind. It is trivially easy to imagine - though not establish that they are - someone who is an authority on whether they themselves have a mind: absolutely anyone with a mind, etc. (I'm just a moron on a forum).
^ you are begging the question if only people claiming to be zombies should be believed, at least if you have not already established their authority or their lack of a mind.
I don't think anyone has shown that all arguments from authority assumes other minds, nor that no-one is an authority on solipsism.
I think it's helpful to first consider some examples where it's clearer whether it's circular or not.
Example 1: "I believe that vaccines are beneficial because experts say so." This does not seem circular. We can in principle debate whether it isn't better to look at the evidence for oneself, whether the experts are in fact experts and trustworthy, etc., but none of this seems to involve circularity.
Example 2: "I believe that one should trust experts because experts say so." This seems very circular. If one doesn't trust experts already, this gives one no reason to trust experts.
So the question is whether your cases are more like example 1 or more like example 2. To me, they certainly don't seem as circular as example 2. But perhaps, for example with your second case, it could be circular -- for example, if the reason you trust experts is that it's the commonsensical thing to do; or perhaps if you are really considering a skeptical hypothesis such as "Is this all just a dream?" (see, e.g., https://press.princeton.edu/books/paperback/9780691128597/dream-death-and-the-self), in which case these experts would just be created by your imagination perhaps precisely in a way to keep you believing in the dream.