Docstoc

12_shifting_the_burden_of_proof

Document Sample
12_shifting_the_burden_of_proof Powered By Docstoc
					The fallacy of shifting the
burden of proof
Lecture 12
Ben Bayer
Philosophy 102: Logic and Reasoning
Overview
   Burden of proof
   Burden-shifting by the argument from ignorance
   Burden-shifting by arbitrary assertions
The burden of proof

   A proof is an argument that establishes that its
    conclusion must be true
      This concept describes what using logic is for

   A standard of proof is a formulation identifying the
    types of facts needed to establish a conclusion on a
    given subject matter.
      This concept describes how we achieve the goal

   The burden of proof is an identification of the party
    obliged to meet the standard of proof
      This names whom is expected to aim at the goal
The burden of proof
   In general: the burden of proof is on the party
    claiming to know something
      Example: In a criminal defense trial, burden of proof is
      on the prosecution to establish guilt of the defendant.
      Example: In science, the burden of proof is on the
      scientist to establish the truth of new scientific claims.
The burden of proof
   Shifting the burden of proof is the fallacy of
    drawing a conclusion from a false assignment of
    burden of proof.
      Example: criminal prosecutors shift the burden of proof
      onto the defendant by claiming he must prove his
      innocence
      Example: scientists shift the burden of proof onto their
      critics by claiming they are right if they haven’t be
      refuted.
Burden-shifting by the argument from
ignorance
   The argument from ignorance is the fallacy of
    shifting the burden of proof by treating ignorance
    as an unconditional source of evidence.
   Type 1: “There’s no proof that X is not so, therefore
    X is so.”
      This is a fallacy because nothing comes from
       nothing!
Burden-shifting by the argument from
ignorance
   Examples of type 1 argument from ignorance:

    You can’t prove your money didn’t come from selling drugs. Therefore
    you must be a drug dealer.


    You ask why I should engage in this risky activity. Well I say, why not?


    No one has ever shown that God does not exist, therefore he does.
Burden-shifting by the argument from
ignorance
   And my favorite example!:
Burden-shifting by the argument from
ignorance
   Exercise:
     Decide  if there is an argument from ignorance fallacy
      involved in the following example:

        There’s no evidence that the sun has gone supernova
        (ceased to exist), therefore it will rise in the morning.

     (Suppose   that the argument is made at night)
Burden-shifting by the argument from
ignorance
   The argument from ignorance is the fallacy of
    shifting the burden of proof by treating ignorance
    as an unconditional source of evidence.
   Type 1: “There’s no proof that X is not so, therefore
    X is so.”
      This is a fallacy because nothing comes from
       nothing!
      Qualification: Absence of proof that X is not so can
       be evidence that X is so, conditioned on
       background knowledge that X was so, and that we
       would know if it had changed.
Burden-shifting by the argument from
ignorance
   Other examples of ignorance as conditional
    evidence:

      I haven’t heard any news in the last few days that the
      President has been assassinated, therefore he must still
      be President.

      This scheming dictator has not shown that he has
      disarmed, therefore he probably still has weapons.
Burden-shifting by the argument from
ignorance
   Type 1: “There’s no proof that X is not so, therefore
    X is so.”
   Type 2: “There’s no proof that X is so, therefore X
    is not so.”
      A fallacy because “absence of evidence is not
       evidence of absence”
Burden-shifting by the argument from
ignorance
   Examples of type 2 argument from ignorance:

    I haven’t heard any prominent news stories about rain falling in the
    south Pacific. Therefore there must be no rain there.


    There are no confirming news reports from the 1960s of hippies spitting
    on returning Vietnam vets, therefore it never happened.


    There is currently no Darwinian explanation for this complex molecule,
    so it must have been designed by God.
Burden-shifting by the argument from
ignorance
   Exercise:
     Decide  if there is an argument from ignorance fallacy
      involved in the following example:

        There is no evidence that there is a large pink elephant in
        this room, so there is no large pink elephant here!
Burden-shifting by the argument from
ignorance
   Type 1: “There’s no proof that X is not so, therefore
    X is so.”
   Type 2: “There’s no proof that X is so, therefore X
    is not so.”
      A fallacy because “absence of evidence is not
       evidence of absence”
      Qualification: Absence of proof that X is so can be
       evidence that X is not so, conditioned on
       background knowledge that if X was so, we would
       know about it.
Burden-shifting by the argument from
ignorance
   Another example of ignorance as conditional
    evidence:

      There is no evidence that Santa Claus exists, so he must
      not.

      (Likewise for many other fictional beings.)
Burden-shifting by arbitrary assertion

   An arbitrary assertion is a claim devised entirely by
    the imagination, but asserted in defiance of the
    need for evidence

       Example: There is an unperceivable gremlin
       dancing on a planet somewhere, leaving no traces.
Burden-shifting by arbitrary assertion

   Arbitrary assertions make the argument from
    ignorance even more destructive
      Example: There is an unperceivable gremlin dancing on a planet
      somewhere, leaving no traces. Prove there isn’t!
      Example: I have secret knowledge that you shot JFK: Prove you didn’t!
     But cannot prove negatives without reference to other
      evidence
        There is no gremlin on Mars, because our probes have photographed
        it and found conditions hostile to life.
        I could not have shot JFK, because I was in New York on November
        22, 1963.
Burden-shifting by arbitrary assertion

   Arbitrary assertions of possibility shift burden of
    proof from burden to provide evidence to burden
    to discount imagination.
     These  can be used to discount any evidence offered to
      falsify some claim
Burden-shifting by arbitrary assertion
   Examples of arbitrary possibilities used to prevent falsification:

       You say our instruments found no gremlins, but maybe the instruments
       were broken, maybe it’s a different kind of life.

       You say you were in New York, but maybe you’re lying, maybe your
       alibis are paid actors.

       Witnesses say they saw a plane crash into the Pentagon, but maybe
       they’re just part of the conspiracy!

       You say you have evidence that the Earth is round. Well maybe those
       ships disappear over the horizon because they sink!
Burden-shifting by arbitrary assertion

   Arbitrary assertions of possibility shift burden of
    proof from burden to provide evidence to burden
    to discount imagination.
     These  can be used to discount any evidence offered to
      falsify some claim
     Scientists sometimes say theories must be “falsifiable” to
      be admissible: really possibilities should be based on
      evidence to begin with, not arbitrary
Burden-shifting by arbitrary assertion

   Recall that proof means ruling out possible
    conclusions consistent with the evidence
     If possibilities are generated by imagination, proof will
      never be possible
     If possibilities must be based on evidence, proof will be
      possible
   We now see that the first kind of possibilities are
    arbitrary
     If arbitrary possibilities are really inadmissible, proof
      may be possible
     It seems we can give evidence for possibilities:
Burden-shifting by arbitrary assertion

   Maybe you’re lying, because people lie and I can
   imagine your lying.
     vs.
   Maybe you’re lying, because you have a reputation for
   dishonesty and I’ve detected a contradiction in your
   story.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:4
posted:7/30/2012
language:English
pages:23