As conflicting as they seem, Panglossianism and Meliorism nevertheless share some common ground. Both positions are normativist: They accept that rationality is measured by conformity to certain normative standards, while disagreeing, at least to an extent, on what those standards are, and how far the conformity exists. It is easy to see that identifying which normative standard is the right one ... [Show full abstract] would have far-reaching consequences for the Panglossians vs. Meliorists debate. Some normative standards may fit human behavior better than others, decreasing the normative-descriptive gap. In particular, the proponents of Bayesian rationality (Oaksford and Chater, 1998, 2007, 2009) suggested that probabilistic norms might provide a better fit to human rationality than norms derived from classical logic. However, arbitrating between normative standards is far from trivial. Elqayam and Evans (2011) criticized normativist theories (Panglossian and Meliorist alike) for trying to base this arbitration on empirical evidence, and so being in danger of committing the dubious inference from is to ought, considered a fallacy by many philosophers (Hudson, 1969; Pigden, 2010).