 The question whether the exceptional status of Penguin relative to flies should spread also to other properties of Bird may depend on specific relevance relations among these properties. For instance,  Koons (2017)  proposes that causal relations play a role: whereas has strong forlimb muscles is causally related to flies and hence should not be attributed to penguins, the situation is different with is cold-blooded. Similarly,  Pelletier and Elio (1994)  argue that explanatory relations play a significant role in the way in which reasoners treat exceptional information in non-monotonic inference. 