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, 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).
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2.
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Reason as slave: Decision Theory
Objective Ethics and Perfect Integrity
Lewis vs Desire As Belief (DAB)
Hájek and Pettit’s Indexical DAB
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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.
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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
 +50
 -100
 -120
0
V
Murder
96%
2%
1%
1%
44.8
Not
Murder
1%
0%
0%
99%
0.5



0
V
Murder
96% +10
2% -140
1% -160
1%
-40
4.8
Not
Murder
1%
0%
0%
99%
0
0.5
+50
Richard C Jeffrey, The Logic of Decision,
University of Chicago Press, 1983


A1, ... , An partition
C(Ai|A) = C(Ai A)/C(A)
if C(A)>0
Richard C Jeffrey, The Logic of Decision,
University of Chicago Press, 1983
“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”



Walter learns more of Phyllis’s past and
becomes suspicious.
Does this mean that she will betray him?
Update C to CE and V to VE
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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 <C,V> is rational so is <CE,VE >
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Murdering Phyllis’ husband was wrong/bad.
Objective ethics
o
A = A is good/right


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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
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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(Ao ) = 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(Ao )
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Necessarily, all agents have perfect integrity,
because there is no more to desiring A than
believing Ao.
Apparent lack of integrity is really a lack of
sincerity.
For any agent with credences C and values V,
DAB
David Lewis. Desire as Belief. Mind, 97:323–332, 1988.
David Lewis. Desire as Belief II. Mind, 105:303–313, 1996.
A
Ao
David Lewis. Desire as Belief. Mind, 97:323–332, 1988.
David Lewis. Desire as Belief II. Mind, 105:303–313, 1996.
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How about
V(A) = C(if A then Ao )
(CCCP) C(if A then B ) = C(B |A)
Lewis: also trivial
?
Huw Price. Defending Desire-as-Belief. Mind, 98 (389):119–127, 1989.
David Lewis. Probabilities of Conditionals and Conditional Probabilities.
Philosophical Review 85: 297-315, 1976.
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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(Ao)
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Allow the meaning of Ao to depend on <C,V>
Too easy (but is that a problem?)
Are any ethical theories indexical?
Alan Hájek, Philip Pettit. Desire Beyond Belief. Australasian Journal of Philosophy,
82(1): 77-92, 2004

Ao = 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
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Candidate Indexical theories:
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I approve of A
In the current circumstances, A
A maximizes my expected happiness
A maximizes expected-by-me happiness
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Indexicality in general
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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
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E.g., Ao determines the set of <a,w> such that a
approves of A in world w.
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Objective ethics presupposes a conception of
integrity (and moral perfection) that is
incompatible with evidential reasoning.