that. Thus the argument is a fallacious one. In symbolic form, the above arguments are Premise 1: I know who X is. Premise 2: I do not know who Y is. Conclusion: Therefore, X is not Y. Note, however, that this syllogism happens in the reasoning by the speaker "I"; Therefore, in the formal modal logic form, it'll be Premise 1: The speaker believes he knows who X is. Premise 2: The speaker believes he does not know who Y is. Conclusion: Therefore, the speaker believes X is not Y.Premise 1 is a very strong one, as it is logically equivalent to . It is very likely that this is a false belief: is likely a false proposition, as the ignorance on the proposition does not imply the negation of it is true. Another example: Premise 1: Lois Lane thinks Superman can fly. Premise 2: Lois Lane thinks Clark Kent cannot fly. Conclusion: Therefore Superman and Clark Kent are not the same person. Expressed in doxastic logic, the above syllogism is: Premise 1: Premise 2: Conclusion: The above reasoning is invalid (not truth-preserving). The valid conclusion to be drawn is . See also Epistemic closure Epistemology Logic in computer science Philosophical ExplanationsNotes References Anderson, A. and N. D. Belnap. Entailment: The Logic of Relevance and Necessity. Princeton: Princeton University Press, 1975. ASIN B001NNPJL8. Brown, Benjamin, Thoughts and Ways of Thinking: Source Theory and Its Applications. London: Ubiquity Press, 2017. . van Ditmarsch Hans, Halpern Joseph Y., van der Hoek Wiebe and Kooi Barteld (eds.), Handbook of Epistemic Logic, London: College Publications, 2015. . A classic reference. Ronald Fagin, Joseph Halpern, Moshe Vardi. "A nonstandard approach to the logical omniscience problem." Artificial Intelligence, Volume 79, Number 2, 1995, p. 203-40. Hendricks, V.F. Mainstream and Formal Epistemology. New York: Cambridge University Press, 2007. . Meyer, J-J C., 2001, "Epistemic Logic," in Goble, Lou, ed., The Blackwell Guide to Philosophical Logic. Blackwell. Montague, R. "Universal Grammar". Theoretica'', Volume 36, 1970, p. 373-398. . . See Chapters 13 and 14; downloadable free online. External links "Epistemic modal logic"—Ho Ngoc Duc. Modal logic Artificial intelligence Formal epistemology