P160 Hempel, Hume, Deduction, and Induction

PHIL 160PHIL 160PHIL 160PHIL 160


Strategy for theorizing & testing

Role of deduction

Role of induction

Problem of induction

Strategy for theorizing & testing

Role of deduction

Role of induction

Problem of induction

SENTENCES IN SCIENTIFIC THEORIES SENTENCES IN SCIENTIFIC THEORIES


SENTENCES DESCRIBING EXPERIENCESENTENCES DESCRIBING EXPERIENCE


True assumptionsguarantee

true conclusion.

True assumptionsguarantee

true conclusion.

DEDUCTIVE LOGICDEDUCTIVE LOGIC

1.All men are mortal.

2.Socrates is a man.

Socrates is mortal.

1.All men are mortal.

2.Socrates is a man.

Socrates is mortal.


True assumptions support (not

guarantee) true conclusion.

True assumptions support (not

guarantee) true conclusion.

INDUCTIVE LOGICINDUCTIVE LOGIC

1.Frog 1 died at time t1.



n. Frog n died at time tn.

All frogs are mortal.




n. Frog n died at time tn.

All frogs are mortal.


Exemplar of good scientific reasoning:

Semmelweis takes on childbed fever

1840s Vienna General Hospital, mothers becoming ill and dying shortly after giving birth.

Death rate 5 times higher in 1st division ward than 2nd division ward.

1st division ward – staffed by physicians & med students

2nd division ward – staffed by midwives.


Semmelweis asks:

•What’s causing childbed fever?

•How can we prevent childbed fever?

•Why more childbed fever in 1st division ward than 2nd division ward?

Strategy: Identify differences between two wards that might explain different death rates.


STRATEGY:STRATEGY:

• Identify phenomenon to explain (childbed fever).

• Find similar settings, one with the phenomenon, the other without.




STRATEGY:STRATEGY:



• Identify differences between settings.

• Test to see which differences are relevant to the phenomenon.



• Identify differences between settings.

• Test to see which differences are relevant to the phenomenon.


Find the difference between wards that explains higher rate of childbed fever in 1st division ward.

Find the difference between wards that explains higher rate of childbed fever in 1st division ward.

Test: changing the difference lowers rate of childbed fever in 1st division ward.

Test: changing the difference lowers rate of childbed fever in 1st division ward.

STRATEGY:STRATEGY:


Deductive ArgumentDeductive Argument

1. If “priest-terror” causes childbed fever, rerouting priest/removing bell will lower childbed fever rate.

2. Rerouting priest/removing bell does not lower childbed fever rate.

“Priest-terror” does not cause childbed fever.





1. If delivering on back causes childbed fever, switching to lateral deliveries will lower childbed fever rate.

2. Switching to lateral deliveries does not lower childbed fever rate.

Delivering on back does not cause childbed fever.

1. If delivering on back causes childbed fever, switching to lateral deliveries will lower childbed fever rate.

2. Switching to lateral deliveries does not lower childbed fever rate.

Delivering on back does not cause childbed fever.Deductive ArgumentDeductive Argument


Inductive ArgumentInductive Argument

1. Much higher rates of childbed fever in wards attended by physicians and medical students than in wards attended by midwives.

Childbed fever must be caused by something physicians and medical students (but not midwives) are exposed to.

1. Much higher rates of childbed fever in wards attended by physicians and medical students than in wards attended by midwives.

Childbed fever must be caused by something physicians and medical students (but not midwives) are exposed to.



1. Childbed fever caused by something physicians and medical students (but not midwives) are exposed to.

2. Physicians and medical students (but not midwives) do autopsies.

3. Kolletschka got childbed fever after an autopsy.

Childbed fever must be caused by something physicians and medical students (but not midwives) are exposed to in autopsies (“cadaveric matter”).

1. Childbed fever caused by something physicians and medical students (but not midwives) are exposed to.

2. Physicians and medical students (but not midwives) do autopsies.

3. Kolletschka got childbed fever after an autopsy.

Childbed fever must be caused by something physicians and medical students (but not midwives) are exposed to in autopsies (“cadaveric matter”).



1. Physicians and medical students pick up cadaveric matter from autopsies.

2. If hands and instruments are washed with chlorinated lime, removes or destroys cadaveric matter.

3. When physicians and medical students wash with chlorinated lime, childbed fever rate in 1st division ward declines.

Cadaveric matter causes childbed fever.






Big AssumptionsBig Assumptions

• Cadaveric matter exists, transmitted from autopsies.

• Chlorinated lime removes or destroys cadaveric matter.

• Cadaveric matter exists, transmitted from autopsies.

• Chlorinated lime removes or destroys cadaveric matter.No one observed cadaveric matter!No one observed cadaveric matter!










Inductive Argument =premises support

conclusion

Inductive Argument =premises support

conclusion

Change that affects outcome.Change that affects outcome.


Did Semmelweis prove his conclusion?Did Semmelweis prove his conclusion?

1. If H is true, then so is I.2. (As the evidence shows) I is true.

H is true.

1. If H is true, then so is I.2. (As the evidence shows) I is true.

H is true.

“fallacy of affirming the consequent”“fallacy of affirming the consequent”

True premises don’t guarantee a true conclusion. (There might be another reason I is true!)

True premises don’t guarantee a true conclusion. (There might be another reason I is true!)


1. If cadaveric matter causes childbed fever, then removing/destroying it by washing with chlorinated lime will reduce rate of childbed fever.

2. (As the evidence shows) washing with chlorinated lime reduces rate of childbed fever.


1. If cadaveric matter causes childbed fever, then removing/destroying it by washing with chlorinated lime will reduce rate of childbed fever.

2. (As the evidence shows) washing with chlorinated lime reduces rate of childbed fever.


Did Semmelweis prove his conclusion?Did Semmelweis prove his conclusion?“fallacy of affirming the consequent”“fallacy of affirming the consequent”


Semmelweis used his observations to find the relevant difference.

His theory led to an effective intervention.

But, the data didn’t prove his conclusion.

Semmelweis used his observations to find the relevant difference.

His theory led to an effective intervention.

But, the data didn’t prove his conclusion.


Where’s the deduction?


1. If H is true, then so is I.2. (As the evidence shows) I is

false. H is false.


false. H is false.

Ruling out potential causes.Ruling out potential causes.









Where’s the deduction?Ruling out potential

causes.Ruling out potential causes.


What’s wrong with induction?What’s wrong with induction?

Supporting potential causes of childbed fever.

Supporting potential causes of childbed fever.1. If H is true, then so is I.2. (As the evidence shows) I is

true. H is true.


true. H is true.

“fallacy of affirming the consequent”“fallacy of affirming the consequent”

Where’s the induction?

Where’s the induction?


All knowledge through experience.All knowledge through experience.

Empiricism:Empiricism:

(Anything I know has backing in empirical data.)

(Anything I know has backing in empirical data.)


Can’t get empirical data about things you haven’t observed!

Can’t get empirical data about things you haven’t observed!

Problem of induction:Problem of induction:

Can’t be certain things you haven’t observed will be like things you have observed!

Can’t be certain things you haven’t observed will be like things you have observed!

P160 Hempel, Hume, Deduction, and Induction

Education

Transcript of P160 Hempel, Hume, Deduction, and Induction