 Non-monotonic logic studies a defeasible consequence relation \(\dproves\) between premises, on the left of the wavy turnstile, and conclusions on the right. One may think of the premise \(\alpha\) on the left as a sentence expressing all the “hard evidence” that an agent may possesses, and the conclusion on the right to be the defeasible conclusions that are justified on the basis of \(\alpha\). The expression \(\alpha \dproves \beta \) may be read as: if my total evidence were \(\alpha\), I would be justified in concluding \(\beta\). Thus a particular relation of defeasible consequence represents an agent's dispositions to update her beliefs in light of new information.