I’ve had a few “Duh!” moments of late
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The online quiz for today’s reading included
questions about “auxiliary assumptions” as
Hempel argued for them – but the editor of our
volume cut out the 2 relevant paragraphs… I
should have caught it! We’ll cover the issue.
On question 20 of the test, you were correct if
you did not choose (b) concerning evidence of
writing. First of all, it wasn’t in the film – and
second, that’s because it comes *much* later!
So your TA will give you the point if you lost one
for not choosing it … and if you did choose it, no
penalty. You’re just up one point.
Let’s talk essays…
 As the material of one link suggests,
philosophical papers often include an
argument for a thesis.
 But, in this essay, your priority is explicating
the reasoning/argument of the scientist or
scientists on whom you focus – how they
reasons from an artifact they can observe to
the existence of some cognitive (mental)
capacity in an ancestor group they cannot
observe.
 You are asked to evaluate the reasoning, but
that is not the main project of this first essay.
Let’s talk essays…
 You may or may not include a brief
introduction. Do so when you believe your
analysis needs some “framing”…
 Describe the artifact you have chosen clearly
(you need not add specific dates proposed for
its age, or place it was found); just what
scientists take it to be (e.g., a decorative bead,
a tool for hunting large animals, a painting…)
 Then outline (not literally…) their argument for
a hypothesis concerning some mental capacity
they think it points to (serves as evidence of).
Let’s talk essays…
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Back to the beads…
Artifact: shells that have been uniformly polished and
“pierced” to allow for hanging/stringing… and many of
them in particular spots.
Evidence that these people were willing to spend
thousands of hours engaging in a project without (at
least obvious) survival value.
Evidence of how they were made, and thus how
labor-intensive the process of making them
Hypothesis: the beads were used to reflect “social
identity”… perhaps “I am a member of this tribe”
Let’s talk essays…
Back to the beads…
 Surely, they serve as evidence for a
hypothesis that at this time in our history,
humans were engaging in activities that
demonstrate creativity and/or artistic
expression… and, perhaps, interest in
symbolizing social identity
 But you might think (as I do) that the move to “I
am a mother of 3”… is something of a leap.
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Let’s talk essays…
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Back to the beads…
So after you’ve laid out the argument for the
hypothesis being offered, you are asked to evaluate
it.
How does one go about doing this when, as in this
case, we cannot directly observe the folks we are
hypothesizing about?
It’s not enough that the hypothesis “would” explain
the artifact…
But ask, rather, whether there are equally plausible
(even one) alternative hypotheses that would work
equally well. Then the reasoning isn’t as strong as it
might first appear.
Let’s talk essays…
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Back to the beads…
So, in the case of the beads, it seems that to assume
they represented social identity beyond just
something like “I belong to this group” is not really
that strong. For alternatives:
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The beads were actually used as barter, and had no more
meaning than that
Or the beads just signaled group membership…
Exist.
And perhaps the social identity hypothesis relies too
much on imposing our way of thinking today on early
ancestors…
“Narrow” (or naïve) inductivism
Collect facts → Categorize them → Generalize
to a hypothesis → Test the hypothesis
Hypothesis
Induction
Facts
Deduction
Facts
Problems
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The problem of induction (which, as empiricists, they
should have known about!)
More importantly, the mismatch between their model of
discovery and actual historical cases of discovery, which
seem to involve (not all at once but regularly)
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Luck
Accidents
“Crazy” reasoning
How to fix these problems?
One answer: give up on an account of “discovery” of
hypotheses or theories
Focus instead on the “logic” of testing them once
discovered – emphasizing, again, logical reasoning and
experience
New approach: Distinguishing between the
contexts of discovery and justification
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Context of discovery
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The reasoning involved in the discovery of
hypotheses or theories.
Inductive? Creative? Luck? Synthesis…?
Any such account should be compatible with the
history and current practice of science.
Context of justification
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The reasoning involved in the testing of hypotheses
or theories.
Deductive, inductive, or something else?
Any such account should be compatible with the
history and current practice of science.
Hempel: The logic of confirmation
Ignaz Semmelweis
“The savior of mothers”
In 1847, identified “putrid”
material and bad hygiene
on the part of medical
practitioners as implicated
in childbed fever
His findings were rejected by
the medical community
He suffered a nervous
breakdown and was
institutionalized
Death reported as a suicide;
turned out to be murder
Hempel’s inductivism (scientific reasoning
is inductive in a “wider sense”)
1.
2.
3.
4.
5.
The identification or recognition of a problem (something
to be explained)
Consideration or generation of hypotheses
Consideration: are proposed hypotheses compatible with
other things we know?
Generation: creativity, accidents, luck… NOT induction or
any other logical process
Choosing one or more hypotheses to test (figuring out
how…)
Tests
Confirmation (inductive!) or falsification (more
complicated than logical argument form suggests)
Hempel’s inductivism (scientific reasoning
is inductive in a “wider sense”)
1.
2.
The identification or recognition of a problem: the case of
Semmelweis as representative
One general problem: Childbed fever
A more specific problem: Why the rates were much
higher in Division One than in Division Two of the
same hospital? (In a sense providing a “natural
experiment”)
Consideration or generation of hypotheses
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Some are already current
Telluric influences, crowding, diet, examination techniques, dread
caused by the priest, delivery position…?
3.
Which ones does he test? And of those he doesn’t, why
not? Which can he test directly? Which indirectly?
Hempel’s inductivism
If childbed fever is caused by telluric influences,
women in both divisions should contract it at
equal rates, as should women who deliver in
home or in the street.
2. Women who deliver in the second division, as
well as women who deliver at home and in the
street, do not contract childbed fever at the same
rate as those in the first division
---------------------------------------------------So, childbed fever is not caused by telluric
influences.
1.
Hempel’s inductivism
The diets are the same in the two divisions
Midwives in the 2nd division use the same
examination techniques as med students in
the 1st division
It’s not due to overcrowding in the 1st division,
as it is the 2nd that is overcrowded
Hempel: The logic of confirmation
If childbed fever is caused by dread brought on
by the priest bringing last rites (here the 2
wards differ), then changing the priest’s route
so women in the 1st division don’t see him will
result in a drop in cases.
2. The priest’s route is changed.
3. There is no drop in cases
---------------------------------------------------Childbed fever is not caused by dread brought on
by the priest bringing last rites.
1.
Hempel: The logic of confirmation
If H, then I
2. Not I
-----------------Not H
Modus Tollens
Deductively valid
Will come to be called “the logic of falsification.
Hempel is himself focusing on “the logic of
confirmation”.
1.
Hempel: The logic of confirmation
If childbed fever is caused by a woman’s
position in delivery (here the 2 wards differ),
then changing women’s positions in the 1st
division should lead to a drop in cases.
2. Women’s positions in the 1st ward are
changed.
3. There is no drop in cases
---------------------------------------------------Childbed fever is not caused by delivery position.
1.
Modus Tollens again.
Hempel: The logic of confirmation
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2.
Semmelweis arrives at his first confirmed
hypothesis because of an accident … the
poisoning of a surgical colleague whose skin
was punctured by a scalpel during an autopsy.
Why think of cadaveric material as a likely
cause?
1.
2.
His colleagues illness was just like that of women who
died of “childbed” fever.
As importantly, only women in the first division were
examined by medical students directly after the students
performed autopsies… and did not wash their hands.
Hempel: The logic of confirmation
If childbed fever is caused by cadaveric material,
then if medical students wash their hands in a
solution of chlorinated lime, there will be a drop
in the number of cases.
2. Medical students wash their hands in the
solution.
3. There is a drop in cases of childbed fever.
---------------------------------------------------So, childbed fever is caused by cadaveric material.
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Hempel’s initial schema
If H, then I1, I2… and In
 I1, I2… and In
---------------------------------- H
Why is this form of argument inductive?
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However many confirmations the hypothesis enjoys, these are finite
in number, and can only show that some hypothesis – which is a
generalization or universal statement – is probable.
We have the same gap that occurs in empirical generalizations…
though the “order” of reasoning is reversed!
And, of course, it turns out the Semmelweis’ initial hypothesis is
wrong (or at least just partial)
1.
Hempel on the problems of confirmation
Yes, confirmation can only demonstrate the
probability of a hypothesis
But every positive test is one which opened the
possibility that the hypothesis would be falsified.
The more confirmations a hypothesis enjoys, the
more warranted we are in (provisionally)
accepting it as the basis for further research.
2.
Moreover deductive logic has its limits as
well…
Even in mathematics or formal logic, deductively
valid arguments or “proofs” do not themselves
dictate any specific conclusion: indeed, an
infinite number of results will follow logically.
Hempel on the problems of confirmation
2.
Moreover deductive logic has its limits as
well…
In logic, for example, we can prove the following:
P
--P or Q (‘or’ is inclusive in logic – at least one is true)
And from ‘P or Q’, we can prove ‘P or Q or R’…
3.
Hempel on the problems of falsification
Moreover deductive logic as used in science
has has a second problem.
Consider the deductively valid argument
form of the logic of falsification (Modus
Tollens)
If P, then Q
Not Q
--------------Not P
or
If H, then I
Not I
-------------Not H
Hempel on the problems of confirmation
Imagine that the experiment went differently:
• If childbed fever is caused by cadaveric material,
then if medical students wash their hands in a
solution of chlorinated lime, there will be a drop
in the number of cases.
• There is no drop.
---------------------------------------------------3. Childbed fever is not caused by cadaveric
material
… but should we conclude that?
After all, there were good reasons to believe it was.
The logic of falsification
1. If
childbed fever is caused by cadaveric
material, then if medical students wash their
hands in a solution of chlorinated lime, there
will be a drop in the number of cases.
2. What might we ask?
Did the medical students wash their hands?
 Did they wash their hands after examining each
patient?
 Was the solution strong enough?
 Does chlorinated lime kill whatever it is that
cadaveric material contains and causes childbed
fever?
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Hempel: Getting a better
understanding of the logic of testing
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It is never just H that yields the prediction I
Auxiliary assumptions such as
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Ceteris paribus (all things being equal)
I’ve identified all the variables that might affect the
outcome of the experiment
Lime solution can kill the infectious agents that cause
childbed fever… Students washed their hands…
[If (H & A1) & (A2… and An)] then I.
 Not I
--------------------------------------------Not (H & A1) & (A2… and An)
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Complications in the logic of testing
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It is never just H that yields the prediction I
A historical case.
Tycho Brahe reasoned:
If the Copernican hypothesis is true, then we
should observe stellar parallax (a change in
the angle of a given star to an observer as the
earth moves).
We do not observe stellar parallax.
-----------------------------------------------------So, the Copernican hypothesis is false.
Complications in the logic of testing
If the Copernican hypothesis is true, then we
should observe stellar parallax (a change in
the angle of a given star to an observer as the
earth moves).
A The stars are close enough that stellar
parallax would be seen by the naked eye.
1. We do not observe stellar parallax.
-----------------------------------------------------So, not (H and A)!
1.
Back to the “logic” of discovery
Hempel cites examples, such as Kekule’s
discovery of the structure of the Benzene
molecule, as evidence that there is no logic to
discovery (nor given testing need we worry
about that)
Other examples that support him:
Alfred Wallace, who also came up with natural
selection as a mechanism that allows evolution,
arrived at the hypothesis during a fever induced
by Malaria…
Then there’s the “legend” of an apple falling on
Newton’s head…
Revisiting discovery
Wasn’t there a logic to Semmelweis’
reasoning and is his reasoning idiosyncratic?
 Problem → Consider hypotheses → Reject
those incompatible with other things we
know → Devise tests of those that survive
the first round → Accept or reject on the
basis of success or failure of predictions →
Revise or abandon hypotheses earlier
confirmed if new evidence warrants it…
 Sometimes, “accidents” only lead a well
prepared mind to a hypothesis…
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Popper: the logic of falsification
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There is no “principle of induction” that will justify
induction or an inductivist account of scientific
method/reasoning
Like Hempel, Popper emphasizes that there is no logic
of discovery, but only a logic of justification (testing)
But, unlike Hempel, Popper argues that the important
logic involved in justification or testing is deductive
and, specifically, the logic of falsification (Modus
Tollens).
Re the distinction between “psychology” and
“epistemology”. Here’s the deal:
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Popper thinks Hume and others got into trouble by
focusing on the empirical question of how, in fact, people
reason… rather than on how they should.