View
226
Download
0
Category
Preview:
Citation preview
7/30/2019 Talbot Cr 04
1/32
Critical Reasoning forBeginners: Four
Marianne TalbotDepartment for Continuing EducationUniversity of OxfordMichaelmas 2009
7/30/2019 Talbot Cr 04
2/32
Last week we learned how toanalyse arguments
and set them out logic-book style
7/30/2019 Talbot Cr 04
3/32
Six steps to analysing an argument:
1. identify the conclusion;2. identify the premises;3. add suppressed premises4. remove irrelevancies;5. remove inconsistent terms;
6. remove cross-references.
7/30/2019 Talbot Cr 04
4/32
We saw that, although we need toparaphrase arguments in order tocomplete these steps
we should not change themeaning of any of the premises or
the conclusion
7/30/2019 Talbot Cr 04
5/32
We also saw that although it is necessaryto bring to bear our understanding of theargument
.it is important not to read into theargument anything that isnt there
..at least implicitly
7/30/2019 Talbot Cr 04
6/32
It is extremely important, in
analysing an argument, not toevaluate the argument
that comes later.
.first we identify the argument
then we evaluate it.
7/30/2019 Talbot Cr 04
7/32
This week we shall be starting to
learn how to evaluate arguments
I was going to start with deduction
and so with validity and truth
but I have decided to start with
induction instead
7/30/2019 Talbot Cr 04
8/32
Inductive arguments are such that.
the truth of their premises
makes the truth of their conclusion
more or less likely
7/30/2019 Talbot Cr 04
9/32
All inductive arguments rely on theprinciple of the uniformity of nature.
and the only arguments for theprinciple of the uniformity of natureare themselves inductive
7/30/2019 Talbot Cr 04
10/32
Types of inductive argument:
inductive generalisations;
causal generalisations; arguments from analogy; arguments from authority.
7/30/2019 Talbot Cr 04
11/32
Inductive generalisations:
The premise identifies acharacteristic of a sample of a
population.
the conclusion extrapolates
that characteristic to the rest of the population.
7/30/2019 Talbot Cr 04
12/32
60% of the voters
sampled said theywould vote for Mr.Many-Promise.
Therefore Mr. Many-Promise is likely towin.
Whenever I have triedto ring BT it has takenme hours to getthrough.
Therefore when I ringBT today it will takehours to get through.
7/30/2019 Talbot Cr 04
13/32
Exercise: which questions would you need tohave answered in order to know whether or not
these are good arguments?
60% of the voterssampled said theywould vote for Mr.Many-Promise.
Therefore Mr. Many-
Promise is likely towin.
Whenever I have triedto ring BT it has takenhours.
Therefore today when
I ring BT it will takehours.
7/30/2019 Talbot Cr 04
14/32
7/30/2019 Talbot Cr 04
15/32
How large is the sample?How many of thosewho would vote inthe election weresampled?
10 out of 1 million?
1000 out of 1million?
How often have I
rung BT in thepast?
Once?About 50 times
7/30/2019 Talbot Cr 04
16/32
How representative is thesample?
Were the voterssampled all female?Over 40? White?Middle class?Known to the personconducting thesurvey?
Have I only ever rungBT on a Sunday?After 10pm? When Iam in a hurry?
7/30/2019 Talbot Cr 04
17/32
Are there anycounterexamples?
Has it ever been thecase that 60% of thesample agreedtheyd vote for someone and yetdidnt?
Have I ever rung BTand succeeded ingetting through firsttime?
7/30/2019 Talbot Cr 04
18/32
Beware informal heuristicsThree of Clubs
Seven of DiamondsNine of DiamondsQueen of HeartsKing of Spades
Ace of Spades
Ace of HeartsAce of ClubsAce of Diamonds
King of Spades
7/30/2019 Talbot Cr 04
19/32
Beware informal heuristicsIn 4 pages of anovel (2000words) how manywords would youexpect to find
ending in ing?
In four pages of anovel (2000words) how manywords would youexpect to find that
include the letter n?
7/30/2019 Talbot Cr 04
20/32
Causal generalisations:
The premise identifies acorrelation between two types of event.
the conclusion states thatevents of the first type causeevents of the second type.
7/30/2019 Talbot Cr 04
21/32
Exercise: which questions would you need tohave answered in order to know whether or not
these are good arguments?
Married men livelonger than singlemen
Therefore beingmarried causes you
to live longer
When air is allowedinto a wound maggotsform
Therefore maggots inwounds are caused
by air being allowedinto the wound
7/30/2019 Talbot Cr 04
22/32
Is the premise true?
Who says marriedmen live longer?
A married man?A woman who wantsto get married?Fred, whose parents
split up when he was5?
Who says maggotsform when air getsinto a wound?A newly qualifiednurse?An elderly doctor?
A scientific study?
7/30/2019 Talbot Cr 04
23/32
How strong is the correlation?
How many marriedmen were observed?
Over how long?
Were unmarried men
observed?
How many cases of maggots formingwere observed?
Were wounds intowhich air was not allowed observed?
7/30/2019 Talbot Cr 04
24/32
Does the causal relation make senseor could it be accidental?
Why would beingmarried cause men tolive longer?
Why would air gettinginto a wound causemaggots to form?
7/30/2019 Talbot Cr 04
25/32
What causes what?
Could it be that beinglong-lived causesmarriage in men?
Or could having thegenes for longevitycause men to getmarried?
Ercould maggotsforming cause the air toget into a wound?
Or could there besomething that causesboth air getting into thewound and maggots toform?
7/30/2019 Talbot Cr 04
26/32
Arguments from analogy take justone example of something.
..and extrapolate from a character
of that example.
. to the character of somethingsimilar
to that thing
7/30/2019 Talbot Cr 04
27/32
The universe is like a pocket-watch
Pocket watches have designers
Therefore the universe must have adesigner
7/30/2019 Talbot Cr 04
28/32
Evaluating arguments from analogy:
are the two things similar?
are they similar in respect of something relevant?
can we find a disanalogy?
7/30/2019 Talbot Cr 04
29/32
Arguments from authority
.take one person or group of persons
who are, or are assumed to be, rightabout some things
.and extrapolate to the claim they are
right about other things
7/30/2019 Talbot Cr 04
30/32
Human rights monitoring organisationsare experts on whether human rightshave been violated.
They say that some prisoners are
mistreated in Mexico.
Therefore some prisoners are mistreated
in Mexico
7/30/2019 Talbot Cr 04
31/32
Evaluating arguments from authority:
Who exactly is the source of information?
Is this source qualified in the appropriatearea?
Is the source impartial in respect of thisclaim?
Do other experts make other claims?
7/30/2019 Talbot Cr 04
32/32
Next week well look at validity and truthbefore turning to the evaluation of deductivearguments
Recommended