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Jeremy Seligman The University of Auckland. “We speak not strictly and philosophically when we talk of the combat of passion and of reason. Reason is,

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Presentation on theme: "Jeremy Seligman The University of Auckland. “We speak not strictly and philosophically when we talk of the combat of passion and of reason. Reason is,"— Presentation transcript:

1 Jeremy Seligman The University of Auckland

2 “We speak not strictly and philosophically when we talk of the combat of passion and of reason. Reason is, and ought only to be, the slave of the passions, and can never pretend to any other office than to serve and obey them” (David Hume, Treatise, Bk. II, Pt. Ill, Sect. III).

3 1. Reason as slave: Decision Theory 2. Objective Ethics and Perfect Integrity 3. Lewis vs Desire As Belief (DAB) 4. Hájek and Pettit’s Indexical DAB

4  Walter desires above all else to be Phyllis' lover and believes her husband to be the only obstacle in his path.  Phyllis desires only the large payout on her husband's accidental death.  Together they concoct an elaborate plan of murder dressed as accidental death.  They both desire the successful completion of each step of the plan.

5  Walter wants to follow the murder plan to the extent to which he believes that it will result in his happy union with Phyllis.  Degree of belief (credence C) and degree of desire (value V) are related.  V( )=50 C( | murder) = 96% V( )x C( | murder) = 48 C( | ¬murder)= 1% V( )x C( | ¬murder) = 0.5

6   -100  -120  0V Murder96%2%1% 44.8 Not Murder 1%0% 99%0.5   0V Murder96% +102% -1401% -1601% Not Murder 1% +500% 99% 00.5 Richard C Jeffrey, The Logic of Decision, University of Chicago Press, 1983

7 Richard C Jeffrey, The Logic of Decision, University of Chicago Press, 1983  A 1,..., A n partition  C(A i |A) = C(A i A)/C(A) if C(A)>0

8 “Reason is, and ought only to be, the slave of the passions, and can never pretend to any other office than to serve and obey them”

9  Walter learns more of Phyllis’s past and becomes suspicious.  Does this mean that she will betray him?  Update C to C E and V to V E

10  Simple Conditionalisation  Special case of Jeffrey Conditionalisation  Only one of the ways of updating ones beliefs and desires in the light of new evidence  Claim: if is rational so is

11  Murdering Phyllis’ husband was wrong/bad.  Objective ethics  A o = A is good/right  A maximizes expected happiness  If things were perfect, A would be true  A follows from certain universal principles  An ideal ethical agent would desire A

12  Objective ethics => ethics is subject to reason  We can have ethical beliefs, to various degrees, and adjust them in the same way that we adjust other beliefs.  C ( A o ) = degree of belief that A is good  Integrity: matching one’s behaviour to one’s beliefs about how one should behave  Perfect integrity: V(A) = C ( A o )

13  Necessarily, all agents have perfect integrity, because there is no more to desiring A than believing A o.  Apparent lack of integrity is really a lack of sincerity.  For any agent with credences C and values V, DAB

14 David Lewis. Desire as Belief. Mind, 97:323–332, David Lewis. Desire as Belief II. Mind, 105:303–313, 1996.

15 David Lewis. Desire as Belief. Mind, 97:323–332, David Lewis. Desire as Belief II. Mind, 105:303–313, AoAo A

16 Huw Price. Defending Desire-as-Belief. Mind, 98 (389):119–127,  How about V ( A ) = C (if A then A o ) ?  (CCCP) C (if A then B ) = C( B | A )  Lewis: also trivial David Lewis. Probabilities of Conditionals and Conditional Probabilities. Philosophical Review 85: , 1976.

17  DAB requires perfect match between desires and beliefs.  Only relative desires are behaviourally significant.  Preference for A over B : V ( A ) > V ( B )  Practical Integrity:  Define h such that h ( V ( A ))= C ( A o )

18  Allow the meaning of A o to depend on Alan Hájek, Philip Pettit. Desire Beyond Belief. Australasian Journal of Philosophy, 82(1): 77-92, 2004  Too easy (but is that a problem?)  Are any ethical theories indexical?

19  A o = A is good/right  A maximizes expected happiness  If things were perfect, A would be true  A follows from certain universal principles  An ideal ethical agent would desire A  Candidate Indexical theories:  I approve of A  In the current circumstances, A  A maximizes my expected happiness  A maximizes expected-by-me happiness

20  Indexicality in general  I am a twin.  It is not snowing here.  We are talking about beliefs and desires.  Index and content  Semantic theory:  Proposition as set of worlds  Proposition as set of index-world pairs  E.g., A o determines the set of such that a approves of A in world w.

21  Objective ethics presupposes a conception of integrity (and moral perfection) that is incompatible with evidential reasoning.


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