Explanatory Unification—Philip Kitcher
Theory has explanatory power. The key is in its acceptance. People saw the potential for explanation
with theory.
Before we accept theories for their empirical adequacy, we accept them for their explanatory power. It
was the other way around van Frassen.
Two examples of explanatory power leading to acceptance before empirical adequacy: Newton and
Darwin.
Explanatory store: if you have a K (set of knowledge) then E(K) is the explanatory store over K.
 K is what we know
 E(K) is the arguments you would accept if you accept K
 The best E(K) is the argument that unites all of K. It explains the most phenomena and is the
simplest.
o i) Prior to…
o ii) Explanatory power of … (new theory to be developed)
o iii) Features of theories
What Newton unified: Objects falling to Earth, tides, planetary motion (all were previously disconnected
and had their own theories). Newton unified them.
What Darwin unified: Spread of characteristics, certain groups having traits that others don’t, the same
kinds of trees appearing on mountains around the world, organisms fitting their environment well,
different parts of the world having organisms that have similar roles, but are kind of different, common
heritance, vestigial organs (used to have a function), how local population now and fossils have a
common origin.
Argument Patterns
 Taking arguments and making them more philosophical (i.e., replacing things with dummy
variables) (p. 335)
o Dummy content lets you see path without getting distracted by content.
 Theory needs to provide formal account of how it works.
 Sometimes you’ll gain insights and sometimes you won’t want to do it again.
 You get an idea of what K means by its pattern.
 Some pattern; both pattern and logical nature have a relation.
 The more stringent an argument is and the more it explains, the better it is.
Explanation as unification
If you accept that a couple of sentences explain a phenomenon, you have to accept similar sentences
that explain similar phenomena.
Decline and fall of the covering law model – Too liberal (includes too many things)
Relation between covering law model and unification – covering law model trying to cash out notion
that explanation is about unification
Motivation of covering law model – maximum understanding with minimal statements
Why do we want to explain?
1. Science matters. So we can explain things.
2. To arbitrate disputes.
To what extent are explanations more abstract activities?
Explanations are not arguments (ontologically). We restrict attention to why-questions: deciding when
an explanation explains why something is true. Explanatory power is a special virtue.
Some arguments are explanations, but not all.
The van Fraassen approach does not fit well in Kitcher’s mind. We accept theories based on explanatory
ability and simplicity.
We are motivated to develop a theory because of its promise of explanatory power. The key feature in
acceptance was potential explanatory power.
Why accepting an explanation requires you to accept it for other phenomena.
One explanation that explains lots is preferred to lots of explanations.
Newton would be obligated to explain why phenomena are different (falling objects and planetary
motion covered by his explanation, but not tides). Possibly tides were affected by something other than
gravity.
You have to explain how a different explanation is sufficiently different. All things being equal why go
with this explanation and not others?
According to Kitcher, if x explains y, you can change x slightly and it should be able to explain a slight
change in y.
Explanation is essentially showing how a phenomenon fits into a broader pattern. An explanation is a
broad and general statement.
Example: Can’t have multiple explanations for student height. Genetics / nutrition for one,
family curse for another, praying to the wrong god for yet another. This is the antithesis of
unification. Explaining one student with genetics means you are committed to explaining it that
way. Exception for cases like native tribes that stretch their necks.
Unification might get tricky in non-linear situations.
Diagram on p. 338
K
∑1
Π11
B1
Π12
Π13
∑2
∑3
Π31
B2
Π32
K – Knowledge (everything we know)
∑ – Explanatory stores – arguments acceptable relative to K
Π – Generating sets – patterns with filling instructions
B – Bases – Best generating set for an explanatory store; best basis
Rules A and B (p.339)
-
Basis of ∑’ is as good as basis of ∑ …
C(∑) proper subset of C(∑’) – conclusions from ∑ proper subset of conclusions from ∑’ (∑’ can tell
you same thing as ∑ and more. )
Basis is best generating set for ∑ (best Π)
Asymmetry, Irrelevance and Accidental Generalization
Asymmetry – Pendulum example. Explaining length in terms of period works only if pendulum is moving.
Still need to explain immobile ones. Can reject by rule B. Explaining length by looking at origins only
works if you have an origin to work with. Better off not explaining.
Irrelevance – Hexing salt example. Saying salt dissolved because it was hexed looks like a good model,
but doesn’t explain why non-hexed salt melts.
Accidental generalization - Baldness and school board example. Could conclude that someone on the
school board is bald because they are on the school board. There are other explanations for cases of
baldness that fit.