The main concern of this paper is the problem of method in De Caelo, which has been recently invigorated by the supposition of Aristotle’s acceptance of two standards of justification. Whereas the φυσικῶς argument comes close to demonstrative knowledge, the εὐλόγως argument relies on more general assumptions and allegedly points towards argumentative justification. With a view to better understanding how empirical criteria for theories, teleological principles, and the resolution of difficulties are laid down to provide as much causal explanations as (...) possible, we take side here in the debate about the very purpose of Aristotle’s using of justification by argument in scientific contexts. Our main claim is that although only reasonable proofs can be worked out in empirically underdetermined domains, this in no way amounts to endorsing an alternative to the norms of inquiry Aristotle upholds in natural science. (shrink)