popper’s deductive predictions, ceteris paribus clause and agm belief revision frank zenker...
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Popper’s Deductive Predictions, Ceteris Paribus Clause
and AGM Belief Revision
Frank Zenker
Calgary, October 2006
04/18/23 2
Two Parts The Thread example
Prediction as a form of Deductive Entail-ment, I & T -> P
Critique
Identifying relevant factors, I, produces a ceteris paribus clause, in testing T.
CP & I & T -> P
Belief revision (AGM-style) on consistent, deductively closed proposition-set Cn(K).
Epistemic Entrench-ment/Minimal Change
Revision of initial conditions in AGM.
Mercury Anomaly
Part IPopper‘s Thread Example
(1) I & T -> P
(2) ~P Ergo ~ (I & T) Falsification (m.p)
(2’) I & ~P Ergo ~T T-Falsification (m.p)
(2’) I & T & ~P Ergo interfering factor Immunization
04/18/23 4
Outline Part I T (Popper) A predicted event is deducible
from laws and initial conditions (alone).
Objection (Canfield and Lehrer): You need laws initial conditions and COMP. Thus, not T. Plus, you can’t have COMP.
Rebuttal (Stegmüller): COMP not needed still. COMP already implied in initial cond.
COMP as list of interfering factors, ceteris paribus clause in theory testing.
04/18/23 5
Popper 1959, § 12 “To give a causal explanation of an event
means to deduce a statement describing it, using as premises of the deduction one or more universal laws, together with certain singular statements, the initial conditions. (…) It is from universal statements in conjunction with initial conditions that we deduce the singular statement. (…) We call this statement a specific or singular prediction.“
04/18/23 6
Popper (1959)
We can say that we have
given a causal explanation of
the breaking of a certain
piece of thread if we have
found that the thread has a
tensile strength of 1 lb. and
that a weight of 2 lbs. was
put on it.
2 lbs.
1 lb.
Objection
Canfield & Lehrer (1961)
04/18/23 8
Enter the Magnet Canfield & Lehrer (1961)
1) L (Tx Wx, Bx) 1´) L (Tx Wx, Bx)
2) Tx Wx 2´) Tx Wx Mx
3) Bx 3´) ---
L = Law
T = Thread
W = Weight
M = Magnet
Mx is consistent with Tx Wx, but with an interfering factor, we would not predict Bx.
04/18/23 9
Reductio this “(…) shows that in prediction the event
E predicted is not deducible from the laws and initial conditions that are the premises of the prediction.” CL (1961:206)
Laws must contain completeness assumptions, COMP, consistent with the antecedent of the law, but inconsistent with the consequent.
Rebuttal
(Coffa 1968)
Lakatos 1978
Stegmüller 1983
04/18/23 11
Stegmüller (11969, 1983:189) “But it is not necessary to raise this
condition [COMP, FZ], to begin with.”
“If a DN-systematization is correct and that means complete, then the negations of those statements which describe ‘interfering factors’ must follow from the class of singular premises, possibly from the ‘global’ hypothesis that the system is closed.”
04/18/23 12
Well Just How
do these negations of statements which describe interfering factors follow?
‘Follow’ in the sense of ‘logically follow’
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Setup I = Initial Conditions
T = Theory
P = Prediction
F = Interfering Factor
Fm = Magnet
(1) I & T -> P
(1’) I & T -> P & ~F ?
Since (2) I -> ~Fm?
How does
‘is a weight of 1 x-unit loaded onto a rope of 0,5 x-unit tensile strength’ imply the absence of, e.g. a magnet?
04/18/23 14
Back to Popper (1959)
We can say that we have
given a causal explanation of
the breaking of a certain
piece of thread if we have
found that the thread has a
tensile strength of 1 lb. and
that a weight of 2 lbs. was
put on it.
2 lbs.
1 lb.
04/18/23 15
What is Weight? Weight = Mass (of Object) x KG
Acceleration (via Gravity) m/s2
Where, at the earth’s surface, Gravity = 9.8 m/s2, unit for mass is the KILOGRAM
“The word ‘weight’ denotes a quantity of the same nature as a ‘force’ [N]”. (Comité International des Poids et Mesures, 15 October
1887)
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What is Tensile Strength?
The limited capacity
to retain structural
integrity, expressible
as a directed force.
Second axiom
F = ma
2 kg
1 kg
04/18/23 17
Force A force of one
NEWTON will accelerate a mass of one KILOGRAM at the rate of one meter/second per second.
2 kg
1 kg
1 NEWTON
2 NEWTONS
Sum: 1 NEWTON, downwards
04/18/23 18
F = ma The force that the thread-suspended
object is subject to in the downward direction depends on its acceleration, i.e., the strength of the gravitational field assumed in this application.
With a magnet on top, the value for mass remains constant, but thereis an additional force. 2 kg
04/18/23 19
Identifying relevant factors If I identify the object below the string as
being of a given weight (rather than a mass), I assume the object is subject only to the force of the gravitational field.
In this sense, being an object of a given weight (vs. mass) precludes the presence of a magnet, just as the force exerted by a now-present magnet would falsify the net-force exerted onto the object.
04/18/23 20
vs. ├ One can always add
forces and, thus, change the net sum of the system.
In a deductive recon-struction, however, adding a hypothesis is useless.
A ├ B A C ├ B2 kg
1 kg
1 N
2 NEWTONS
1,2 N
04/18/23 21
Hence, It is not the initial conditions that exclude
the presence of interfering factors.
Rather, exclusion of interfering factors is a function of having formed the sum, i.e., of having assumed a particular finite number of relevant factors (CP).
Assumption is relevant in theory testing, but has no logical form in I & T -> P.
04/18/23 22
Calculating P vs. Testing C The schema
‘I & T -> P’ reads:
‘If I and T are true, then P’.
This is calculating P.
If one adds factors, I and T remain true.
The schema ‘CP & I & T -> P’ reads
‘If I & T is all that is true, then P’.
This is testing T.
Hypotheses, H, make CP false and imply ~P.
‘CP & I & T -> P’, ‘~ P’ Ergo ‘~CP & H’
Part II
04/18/23 24
Outline Epistemic Entrenchment -- AGM axioms
Rationality postulate -- Minimal Change
Applied to the Test of one Empirical Theory
Law: x [Fx -> Gx], Instance: Fa -> Ga
Initial values: Fa, Ceteris paribus clause: CP
Falsific./ Immuniz.: Aux-Hypotheses
Case: Mercury‘s perihelion shift.
AGMAlchorrón, C., Gärdenfors, P. & Makinson, D. (1985). On the
logic of theory change. Partial meet contraction functions and their associated revision functions. Journal of Symbolic Logic 50, 510-530.
Peter Gärdenfors (1988). Knowledge in Flux. Cambridge: CUP.
--- (2000). Conceptual Spaces. Cambridge: MIT Press.
04/18/23 26
AGM (late 1980s) State of Knowledge/Belief, K, as deduct-
ively closed set of propositions, Cn (K)…
…with an EE-ordering that determines comparative retractability (Rott) of items.
Prioritized belief revision. The new and inconsistent belief/ propositions, ~p, must be integrated in a conservative way.
04/18/23 27
AGM Revision Functions K + p = Cn(K {p}) [Expansion]
Whatever is consistent can be integrated.
K p = Cn(K {p}) [Contraction]If p is inconsistent with Cn(K), the least entrenched item in K is deleted „to make room“ (minimal change principle).
K * p = Cn(K {p}) + p [Revision]Contraction before revision.
04/18/23 28
EE-Postulates (EE1) Transitivity
For any A, B and C, if A ≤ B and B ≤ C, then A ≤ C.
(EE2) Dominance
For any A and B, if A |- B, then A ≤ B
(EE3) Conjunctiveness
For all A and B in K, A ≤ A B or B ≤ A B.
(EE4) Minimality
When K = K, A K iff A ≤ B for all B
(EE5) Maximality
If B < A for all B, then |- A.
04/18/23 29
Applying the EE-Postulates Yields an ordering exclusively determined
by deductive relations in K.
If one were to map law, x [Fx -> Gx], instance, Fa -> Ga, and initial values, Fa, accordingly, what ordering do we get?
What determines the identity of the least entrenched belief, i.e., of the deletion-candidate?
04/18/23 30
Handout
04/18/23 31
Handout
04/18/23 32
Thus Both an immunization and a falsification
strategy can be described as obeying the minimal change principle.
The belief to be given up depends only on the pre-ordering. Thus, minimal change is general…and empty.
AGM epistemic entrenchment does not model tenacity of a law (Feyerabend).
Ceteris Paribus
1. Fa -> Ga, Fa therefore Ga
2. CP (Fa -> Ga), Fa & CP therefore Ga
04/18/23 34
Pre-Conceptions We read ‚ceteris paribus‘ propositionally,
i.e., as all other things being equal (absent, negligible).
CP as infinite non-existence statement.
It is never the case that all other things are equal. Moreover, equal to what?
However, we cannot test a theory without taking a verdict on the CP clause.
04/18/23 35
CP as „hypotheses-storage“ If a prediction fails, one can reject CP and
„draw auxilliary hypotheses from it“.
The CP clause is usually not well-corroborated. Read: It is least entrenched!
The deductive schema of theory testing is a schema created by criticism. It eliminates the auxilliary hypotheses and relegates them to background knowledge.
Lakatos (1978)
Mercury Anomaly
Roughly 1857 through 1915
04/18/23 37
Completeness Clause CP & Fa & (Fa -> Ga) therefore Ga.
Every application of an empirical theory T must assume (the truth of) a provisoe that, in a given case, no factors other than those specified in the antecedent(-statement) are present which could affect the event described in the consequent(-statement).
Hempel (1988)
04/18/23 38
Example
Deterministic law of succession
Stellar-System at t1
System at t2
predicted
„observed“
unaccounted factor
04/18/23 39
A very small deviance Mercury orbits the sun once in three months.
Mercury‘s perihelion takes one Platonic year (260 000 years) and describes a „rosette“.
Mercury
PerihelionSun
04/18/23 40
Partial Explanation: 39’’ missingGravitational influence on Mercury
Venus 280’’.6 Jupiter 152’’.6
Earth 83’’.6 Saturn 7’’.2
Mars 2’’.6 Uranus 0’’.1
Total 526’’.7 Observed: + 39”
(Le Verrier 1859:11, after Roseveare 1982:11).
04/18/23 41
Stick to the law!
There is a rule in philosophy… that admits
of no dispute… we are never entitled to
challenge the universality of laws that,
within our experience, have nowhere failed
– until every other mode of overcoming the
difficulty has proved of no avail.
Nichol (1848:63f.), after Musgrave (1976)
04/18/23 42
The classic Immunization Example
Obeying normal-science conservativity, matter hypothesis exploiting pertubation were forwarded.
(i) Vulkan, (ii) belt of asteroids, (iii) matter distribution that causes zodiac-light.
Each is less testable than its predecessor.
As late as the 1950s, „matter was sought“, though Einstein gave the correct orbit.
04/18/23 43
Matter-Hypotheses
Vulkan?
AsteroidsZodiac-Light
CP as least entrenched belief -- AGM-style
Testing a Theory vs.
Calculating a Prediction.
04/18/23 45
CP as least entrenched beliefK Cn(K)
n p v ~p
+1 x Fx->Gx Fa -> Ga
+2 Fa
+3 CP CP & Fa & (CP & Fa ->Ga) Ga
04/18/23 46
Step by Step Prediction
CP & Fa & (CP & Fa -> Ga) |- Ga. Observation
Fa & Ga‘ (where Ga‘ |- ~Ga) Question
CP? (where ~CP |- ~Ga) Immunization
~CP (where H |- ~CP) New Prediction
CP2 & H & Fa & (CP2 & Fa & H -> Ga‘) |- Ga‘
04/18/23 47
Merits The CP clause‘s role as a necessary
completeness assumption in theory-testing finds a logical representation.
New hypotheses „drawn from“ CP, raise its index, indicating severity of an anomaly.
With CP appearing at the level of the applied law-instance, tenacity of law vs. applied instance can be respected (Klee).
Thank you.