"Formal Semantics: Origins, Issues, Early Impact". Baltic International Yearbook of Cognition, Logic and Communication. This Proceeding of the Symposium for Cognition, Logic and Communication. Vol. 6. 2011.
philpapers.org
Lewis, David K. (1973). "4. Foundations". Counterfactuals. Blackwell.
Berto, Francesco; Jago, Mark (2018). "Impossible Worlds". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved 14 November 2020.
Menzel, Christopher (2017). "Possible Worlds". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. Retrieved 14 November 2020.
See "A Priori and A Posteriori" (author: Jason S. Baehr), at Internet Encyclopedia of Philosophy: "A necessary proposition is one the truth value of which remains constant across all possible worlds. Thus a necessarily true proposition is one that is true in every possible world, and a necessarily false proposition is one that is false in every possible world. By contrast, the truth value of contingent propositions is not fixed across all possible worlds: for any contingent proposition, there is at least one possible world in which it is true and at least one possible world in which it is false." Accessed 7 July 2012.
wikisource.org
en.wikisource.org
Arthur Schopenhauer, "Die Welt als Wille und Vorstellung," supplement to the 4th book "Von der Nichtigkeit und dem Leiden des Lebens" p. 2222, see also R.B. Haldane and J. Kemp's translation "On the Vanity and Suffering of Life" pp 395-6
