Combining Texts

All the ideas for 'Leibniz: Guide for the Perplexed', 'Paradoxes of the Infinite' and 'Ways Worlds Could Be'

unexpand these ideas     |    start again     |     specify just one area for these texts

---

4 ideas

4. Formal Logic / F. Set Theory ST / 1. Set Theory

9987	An aggregate in which order does not matter I call a 'set' [Bolzano]
	Full Idea: An aggregate whose basic conception renders the arrangement of its members a matter of indifference, and whose permutation therefore produces no essential difference, I call a 'set'.
	From: Bernard Bolzano (Paradoxes of the Infinite [1846], §4), quoted by William W. Tait - Frege versus Cantor and Dedekind IX
	A reaction: The idea of 'sets' was emerging before Cantor formalised it, and clarified it by thinking about infinite sets. Nowadays we also have 'ordered' sets, which rather contradicts Bolzano, and we also expect the cardinality to be determinate.

6. Mathematics / A. Nature of Mathematics / 5. The Infinite / a. The Infinite

10856	A truly infinite quantity does not need to be a variable [Bolzano]
	Full Idea: A truly infinite quantity (for example, the length of a straight line, unbounded in either direction) does not by any means need to be a variable.
	From: Bernard Bolzano (Paradoxes of the Infinite [1846]), quoted by Brian Clegg - Infinity: Quest to Think the Unthinkable §10
	A reaction: This is an important idea, followed up by Cantor, which relegated to the sidelines the view of infinity as simply something that could increase without limit. Personally I like the old view, but there is something mathematically stable about infinity.

9. Objects / B. Unity of Objects / 2. Substance / d. Substance defined

19347	Substance needs independence, unity, and stability (for individuation); also it is a subject, for predicates [Perkins]
	Full Idea: For individuation, substance needs three properties: independence, to separate it from other things; unity, to call it one thing, rather than an aggregate; and permanence or stability over time. Its other role is as subject for predicates.
	From: Franklin Perkins (Leibniz: Guide for the Perplexed [2007], 3.1)
	A reaction: Perkins is describing the Aristotelian view, which is taken up by Leibniz. 'Substance' is not a controversial idea, if we see that it only means that the world is full of 'things'. It is an unusual philosopher wholly totally denies that.

10. Modality / E. Possible worlds / 2. Nature of Possible Worlds / a. Nature of possible worlds

15432	Structural universals might serve as possible worlds [Forrest, by Lewis]
	Full Idea: Forrest proposed that structural universals should serve as ersatz possible worlds.
	From: report of Peter Forrest (Ways Worlds Could Be [1986]) by David Lewis - Against Structural Universals 'Intro'
	A reaction: I prefer powers to property universals. Perhaps a possible world is a maximal set of co-existing dispositions?