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10. Modality / D. Knowledge of Modality / 3. A Posteriori Necessary

[knowing what has to be, by means of experience]

10 ideas

8856	Quine's indispensability argument said arguments for abstracta were a posteriori [Quine, by Yablo]
	Full Idea: Fifty years ago, Quine convinced everyone who cared that the argument for abstract objects, if there were going to be one, would have to be a posteriori in nature; an argument that numbers, for example, are indispensable entities for 'total science'.
	From: report of Willard Quine (On What There Is [1948], §1) by Stephen Yablo - Apriority and Existence
	A reaction: This sets the scene for the modern debate on the a priori. The claim that abstractions are indispensable for a factual account of the physical world strikes me as highly implausible.

2796	For Quine the only way to know a necessity is empirically [Quine, by Dancy,J]
	Full Idea: Quine argues that no necessity can be known other than empirically.
	From: report of Willard Quine (works [1961]) by Jonathan Dancy - Intro to Contemporary Epistemology 14.6

5476	Essentialists say natural laws are in a new category: necessary a posteriori [Ellis]
	Full Idea: Essentialists do not accept the standard position, which says necessity is a priori, and contingency is a posteriori. They have a radically new category: the necessary a posteriori. The laws of nature are, for example, both necessary and a posteriori.
	From: Brian Ellis (The Philosophy of Nature: new essentialism [2002], Ch.6)
	A reaction: Based on Kripke. I'm cautious about this. Presumably God, who would know the essences, could therefore infer the laws a priori. The laws may follow of necessity from the essences, but the essences can't be known a posteriori to be necessary.

9174	It is necessary that this table is not made of ice, but we don't know it a priori [Kripke]
	Full Idea: Although the statement that this table (if it exists at all) was not made of ice, is necessary, it certainly is not something that we know a priori.
	From: Saul A. Kripke (Identity and Necessity [1971], p.180)
	A reaction: One of the key thoughts in modern philosophy. Kit Fine warns against treating it as a new and exciting toy, but it is a new and exciting toy. Scientific essentialism, which I so want to be true, is built on this proposal.

2408	Kripke has demonstrated that some necessary truths are only knowable a posteriori [Kripke, by Chalmers]
	Full Idea: Kripke has demonstrated the existence of necessary truths such as "water is H2O" whose necessity is only knowable a posteriori.
	From: report of Saul A. Kripke (Naming and Necessity lectures [1970]) by David J.Chalmers - The Conscious Mind 2.4.2

4960	"'Hesperus' is 'Phosphorus'" is necessarily true, if it is true, but not known a priori [Kripke]
	Full Idea: An identity statement between names (such as 'Hesperus' and 'Phosphorus'), when true at all, is necessarily true, even though one may not know it a priori.
	From: Saul A. Kripke (Naming and Necessity lectures [1970], Lecture 3)
	A reaction: This seems correct, but one should not read too much into it. What should we say if Venus fissions into two, one for the morning, one for the evening? That identity implies x=x doesn't prove the existence of unchanging essences.

4966	Theoretical identities are between rigid designators, and so are necessary a posteriori [Kripke]
	Full Idea: Theoretical identities, according to the conception I advocate, are generally identities involving rigid designators and therefore are examples of the necessary a posteriori.
	From: Saul A. Kripke (Naming and Necessity lectures [1970], Lecture 3)
	A reaction: This doesn't open up a huge new realm of a posteriori necessity. We just cured some of our ignorance. I remain unconvinced that the Morning Star is necessarily the Evening Star, except in the boring way that if it is, it is. Venus could fission.

14631	How can you show the necessity of an a posteriori necessity, if it might turn out to be false? [Jackson]
	Full Idea: If something is offered as a candidate necessary a posteriori truth, how could we show that it is necessary, in the face of the fact that it takes investigation to show that it is true, and so, in some sense, it might have turned out to be false?
	From: Frank Jackson (Possible Worlds and Necessary A Posteriori [2010], 1)
	A reaction: This is the topic of his paper, which he compares with how we can know that essences are essential.

16421	Critics say there are just an a priori necessary part, and an a posteriori contingent part [Stalnaker]
	Full Idea: Critics say there are no irreducible a posteriori truths. They can be factored into a part that is necessary, but knowable a priori through conceptual analysis, and a part knowable only a posteriori, but contingent. 2-D semantics makes this precise.
	From: Robert C. Stalnaker (Conceptual truth and metaphysical necessity [2003], 1)
	A reaction: [Critics are Sidelle, Jackson and Chalmers] Interesting. If gold is necessarily atomic number 79, or it wouldn't be gold, that sounds like an analytic truth about gold. Discovering the 79 wasn't a discovery of a necessity. Stalnaker rejects this idea.

15171	The necessary a posteriori is statements either of identity or of essence [Sidelle]
	Full Idea: The necessary a posteriori crudely divides into two groups - (synthetic) identity statements (between rigid designators), and statements of essential properties. The latter is either statements of property identity, or of the essences of natural kinds.
	From: Alan Sidelle (Necessity, Essence and Individuation [1989], Ch.2)
	A reaction: He cites Kripke's examples (Hesperus,Cicero,Truman,water,gold), and divides them into the two groups. Helpful.