Editing Gottfried Wilhelm Leibniz (section)

=== Principles ===<!--Linked from "Difference (philosophy)"-->
Leibniz variously invoked one or another of seven fundamental philosophical Principles:<ref>Mates (1986), chpts. 7.3, 9</ref>
* [[Identity (mathematics)|Identity]]/[[contradiction]]. If a proposition is true, then its negation is false and vice versa.
* [[Identity of indiscernibles]]. Two distinct things cannot have all their properties in common. If every predicate possessed by ''x'' is also possessed by ''y'' and vice versa, then entities ''x'' and ''y'' are identical; to suppose two things indiscernible is to suppose the same thing under two names. The "identity of indiscernibles" is frequently invoked in modern logic and philosophy. It has attracted the most controversy and criticism, especially from corpuscular philosophy and quantum mechanics. The [[converse (logic)|converse]] of this is often called ''Leibniz's law'', or the ''indiscernibility of identicals'', which is mostly uncontroversial. 
* [[principle of sufficient reason|Sufficient reason]]. "There must be a sufficient reason for anything to exist, for any event to occur, for any truth to obtain."<ref>Loemker 717</ref>
* [[Pre-established harmony]].<ref>See Jolley (1995: 129–131), Woolhouse and Francks (1998), and Mercer (2001).</ref> "[T]he appropriate nature of each substance brings it about that what happens to one corresponds to what happens to all the others, without, however, their acting upon one another directly." (''Discourse on Metaphysics'', XIV) A dropped glass shatters because it "knows" it has hit the ground, and not because the impact with the ground "compels" the glass to split.
* [[Law of continuity]]. ''[[Natura non facit saltus]]''<ref name="Saltus">Gottfried Leibniz, [[New Essays on Human Understanding|''New Essays'']], IV, 16: "''la nature ne fait jamais des sauts''". ''Natura non-facit saltus'' is the Latin translation of the phrase (originally put forward by [[Carolus Linnaeus|Linnaeus]]' ''[[Philosophia Botanica]]'', 1st ed., 1751, Chapter III, § 77, p. 27. See also {{Cite SEP|url-id=continuity/|title=Continuity and Infinitesimals|date=Mar 16, 2022|edition=Spring 2022|last=Bell|first=John L.}} See also [[Alexander Baumgarten]], ''Metaphysics: A Critical Translation with Kant's Elucidations'', Translated and Edited by Courtney D. Fugate and John Hymers, Bloomsbury, 2013, "Preface of the Third Edition (1750)", [https://books.google.com/books?id=Jw-Q3hfXTqoC&q=%22must+also+have+in+mind+Leibniz%27s+%22natura+non+facit+saltus%22+%5Bnature+does+not%22&pg=PA79 p. 79 n.d.<!--footnote alphabet-number-->]: "[Baumgarten] must also have in mind Leibniz's "''natura non-facit saltus'' [nature does not make leaps]" ([[Nouveaux essais sur l'entendement humain|NE]]<!--the abbreviation is not italicized in the original--> IV, 16)."). A variant translation is "''natura non-saltum facit''" (literally, "Nature does not make a jump") ({{cite book|last1=Britton|first1=Andrew|url=https://books.google.com/books?id=goW6JsEUz4EC|title=Ökonomische Theorie und christlicher Glaube|last2=Sedgwick|first2=Peter H.|last3=Bock|first3=Burghard|publisher=LIT Verlag Münster|year=2008|isbn=978-3-8258-0162-5|page=289}} [https://books.google.com/books?id=goW6JsEUz4EC&pg=PA289 Extract of page 289].)</ref> (literally, "Nature does not make jumps").
* [[Philosophical optimism|Optimism]]. "God assuredly always chooses the best."<ref>Loemker 311</ref>
* [[Principle of plenitude|Plenitude]]. Leibniz believed that the best of all possible worlds would actualize every genuine possibility, and argued in ''Théodicée'' that this best of all possible worlds will contain all possibilities, with our finite experience of eternity giving no reason to dispute nature's perfection.<ref>[[Arthur Lovejoy]], ''The [[Great Chain of Being]]''. Harvard University Press, 1936, Chapter V "Plenitude and Sufficient Reason in Leibniz and Spinoza", pp.&nbsp;144–182.</ref>

Leibniz would on occasion give a rational defense of a specific principle, but more often took them for granted.<ref>For a precis of what Leibniz meant by these and other Principles, see Mercer (2001: 473–484). For a classic discussion of Sufficient Reason and Plenitude, see Lovejoy (1957).</ref>