This is just one of many potential objections. I chose it arbitrarily. It gives me an excuse for sharing a fun fact about Ellsberg himself, which illustrates how research in decision making has had life-or-death consequences.
[^sug] There are some interesting and influential considerations in Sugden (1991), but this is not the place to start so I recommend considering it only if you already have a good understanding of decision theory and comparatively straightforward objections.
It is perhaps tempting, initially, to think that the objections are simple. They show that decision theory is wrong, misguided or at least too limited to characterise the full richness of human behaviour. But, as we will eventually see, things are much more interesting than that. For it turns out that whether something is an objection depends on what you are using decision theory for.
A preference relation is independent of irrelevant alternatives exactly if ‘no change in the set of candidates (addition to or subtraction from) [can] change the rankings of the unaffected candidates.’ (Dixit, Skeath, & Reiley, 2014, p. 600)
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Jeffrey, R. C. (1983). The logic of decision, second edition. Chicago: University of Chicago Press.
Jia, R., Furlong, E., Gao, S., Santos, L. R., & Levy, I. (2020). Learning about the Ellsberg Paradox reduces, but does not abolish, ambiguity aversion. PLOS ONE, 15(3), e0228782. https://doi.org/10.1371/journal.pone.0228782
Mandler, M. (2001). A difficult choice in preference theory: Rationality implies completeness or transitivity but not both. In E. Millgram (Ed.), Varieties of practical reasoning (pp. 373–402). Cambridge, Mass: MIT Press.