The normal way of understanding priors is that they are or can be expressed as joint probability distributions, which can be more or less well-calibrated. You're skipping over a lot of inferential steps.
Right. We could talk of quality of an approximation to a fixed object that is defined as the topic of a pursuit, even if we can't choose the fixed object in the process and thus there is no sense in having preferences about its properties.
This is our monthly thread for collecting these little gems and pearls of wisdom, rationality-related quotes you've seen recently, or had stored in your quotesfile for ages, and which might be handy to link to in one of our discussions.