Logic by linzhengnd


• The Science (or Art) of Evaluating
      The Basics of Argument
• Argument; “a series of statements, one or
  more of which (premises) are claimed to
  provide support for one of the others (the
• In a “good” argument, the premise(s)
  provide(s) support for the conclusion
• In a “bad” argument the premises do not
  support the conclusion.
             A “statement” is:
• A declarative sentence or clause that
  contains a falsifiable representation of fact.
  – E.g.
     • Wenzel has terrible taste in clothes.
     • It is imperative that the U.S. build a missile defense
     • Canada is in Eastern Europe.
     • Water is a universal solvent.
     Non “statements” include:
• Questions: Where did you get that awful
• Proposals: Let’s find a stylist that can undo
  some of the damage.
• Suggestions: I suggest you fix that before
  you let yourself be seen in public.
• Commands: My husband’s home, hide in
  the closet.
   Two categories of statements
• Premises – statements of fact that provide
  evidence or reasons.
• Conclusions – a statement that the evidence
  or reason is supposed to support or imply.
       A simple argument:
The possibility of nuclear weapons in the
hands of rouge states poses great danger to
the safety of the United States. An anti-
ballistic missile system offers protection
from the threat of ballistic missiles.
Therefore, the nation must build a missile
defense system.
          Conclusion Indicators
•   Therefore              •   Entails that
•   Wherefore              •   Hence
•   Thus                   •   It follows that
•   Consequently           •   Implies that
•   Accordingly            •   As a result
•   We may conclude that
•   so
            Premise indicators
•   Since                  •   Given that
•   As indicated by        •   Seeing that
•   Because                •   For the reason that
•   For                    •   Inasmuch as
•   In that                •   Owing to
•   May be inferred form
•   As
                     Evaluating a Simple Argument

The possibility of nuclear weapons in the hands of rouge states poses great danger
   to the safety of the United States. An anti-ballistic missile system offers
   protection from the threat of ballistic missiles. Therefore, the nation must build
   a missile defense system.

P1: The possibility of nuclear weapons in the hands of rouge states poses great
    danger to the safety of the United States.

P2: An anti-ballistic missile system offers protection from the threat of ballistic

C: Therefore, the nation must build a missile defense system.
                       Analyzing Simple Arguments I
Since the good, according to Plato, is that which furthers a person’s real interests, it follows
    that in any given instance when the good is known, men will seek it.
As the denial or perversion of justice by the sentences of courts, as well an in any other
    manner, is with reason classed among the just causes of war, it will follow that the
    federal judiciary ought to have cognizance of all causes in which the citizens of other
    countries are concerned. (Hamilton, The Federalist No. 80. )
Punishment, when speedy and specific , may suppress undesirable behavior, but it cannot
   teach or encourage desirable alternatives. Therefore, it is crucial to use positive
   techniques to model and reinforce appropriate behavior that the person can use in place
   of the unacceptable response that has been suppressed. (Mischel and Mischel,
   Essentials of Psychology)
To every existing thing God wills some good. Hence, to love any thing is nothing else than
    to will good to that thing, it is manifest that God loves everything that exists. (Aquinas,
    Summa Theologica)
Poverty offers numerous benefits to the nonpoor. Antipoverty programs provide jobs for
   middle-class professionals in social work, penology and public health. Such workers’
   future advancement is tied to the continual growth of bureaucracies dependent on the
   existence of poverty. (Palen, Social Problems)
                  Analyzing Simple Arguments I (cont)

If a piece of information is not “job relevant,” then the employer is not entitled qua
     employer to know it. Consequently, since sexual practices, political beliefs,
     associational activities, etc., are not part of the description of most jobs, that is, since
     they do not directly affect one’s job performance, the are not legitimate information for
     an employer to know in the determination of the hiring of a job applicant. (Brentken,
     “Privacy, Polygraphs and Work”)
Anyone familiar with our prison system knows that there are some inmates who behave little
     better than brute beasts. But the very fact that these prisoners exist is a telling argument
     against the death penalty. If the death penalty had been a truly effective deterrent, such
     prisoners would long ago have vanished. (“The Injustice of the Death Penalty,”
Since the secondary light [from the moon] does not inherently belong to the moon, and is not
     received from any star or from the sun, and since in the whole universe there is no other
     body left but the earth, what must we conclude? What is to be proposed? Surely we must
     assert that the lunar body (or any other dark and sunless orb) is illuminated by the earth.
     (Galilei, The Starry Messenger)
Neither a borrower not a lender be, For loan oft loses both itself and friend, And Borrowing
     dulls the edge of husbandry. (Shakespeare, Hamlet)
The possibility of nuclear weapons in the hands of rouge states poses great danger to the
     safety of the United States. An anti-ballistic missile system offers protection from the
     threat of ballistic missiles. Therefore, the nation must build a missile defense system.
                              Simple Arguments II
University administrators know well the benefits that follow notable success in college
    sports: increased applications for admissions [sic], increased income from licensed logo
    merchandise, more lucrative television deals, post-season game revenue and more
    successful alumni fund drives. The idea that there is something ideal and pure about the
    amateur athlete is self-serving bunk. (anon letter to and editor)
College is a time in which a young mind is supposed to mature and acquire wisdom, and one
    can only do this by experiencing as much diverse intellectual stimuli as possible. A
    business student may be a whiz at accounting, but has he or she ever experienced the
    beauty of a Shakespearean sonnet or the boundless events of Hebrew history? Most
    likely not. While many of these neoconservatives will probably go on to be financially
    successful, they are robbing themselves of the true purpose of collegiate academics, a
    sacrifice that outweighs future salary checks. (Griffith, “Conservative College Press.”)
At a time when our religious impulses might help heal the pains and strains in our society,
    today’s television pulpiteers preach intolerance, censure, and discrimination. They
    package a “believer life-style,” and rail against everyone who doesn’t fit it –
    homosexuals, communists, Jews, and other non-Christians, sex educators and so on.
    Such intolerance threatens to undermine the pluralism that marks our heritage, The
    packaging of that intolerance in slick Hollywood programming or under the guise of
    patriotic fervor is skillfully accomplished on many fronts. That, however, does not make
    it right. (Kreitler, “TV Preachers’ Religious Intolerance”)
                              Simple Arguments II
Most of the environmental Problems facing us stem, at least in part, from the sheer number
   of Americans. The average American produces three quarters of a ton of garbage every
   year, consumes hundreds of gallons of gasoline and uses large amounts of electricity
   (often from a nuclear power plant, coal burning, or a dam). The least painful way to
   protect the environment is to limit population growth. (anon, letter to an editor)
       Identifying Arguments
• Conditions for the presence of an argument:
  – “One of the statements must claim to present
    evidence of something.”
  – “There must be a claim that the alleged
    evidence provides support for or the
    implication of something.”
• For our purposes, the truth value of the
  statements is immaterial. All that matters is
  that a claim be made or implied.
            Types of Claims
• Factual – Condition 1 on the preceding
  slide. Relatively easy to identify.

• Inferential – Condition 2 on the preceding
  slide. More difficult to isolate. The passage
  expresses a reasoning process, that one or
  more elements in the passage supports a
     Types of Inferential Claims
• Explicit – Usually asserted by a premise or
  conclusion indicator.
   – E.g. The human eye can see a source of light as faint as an ordinary candle
     at a distance of 27 kilometers, through a non-absorbing atmosphere. Thus,
     a power searchlight directed from a new moon should be visible on earth
     to the naked eye. (Papalia and Olds, Psychology)
• Implicit – May not include indicator words.
   – E.g. The price reduction[seen with the electronic calculator] is the result
     of of a technological revolution. The calculator of the 1960s used
     integrated electronic circuits that contained about a dozen transistors or
     similar components on a single chip. Today, mass produced chips, only a
     few millimeters square, contain several thousand such components.
     (Biokess and Edelson, Chemical Principles)
       Arguments that Aren’t
• The mere presence of indicator words in a
  sentence does not guarantee that an
  argument is present.
• Compare
  – Since Edison invented the phonograph, there
    have been many technological advances.
  – Since Edison invented the phonograph, he
    deserves credit for a major technological
     Types of Non-Arguments
• Simple Non-Inferential Passages (lack a
  claim of proof)
  – Warnings – unsupported expressions intended
    to put someone on notice of a possible danger
     • Be careful on the train to Comiskey Park.
  – Advice – recommendations for future conduct
     • If you take a course from Wenzel get several sets of
       earplugs and stock up on NoDoz.
   Simple Non-Inferential Passages (cont).

– Statements of opinion – unsupported statements
  of the author’s (or someone else’s) belief(s).
   • A nation with a high moral tradition has an
     obligation to ensure that education is available to all
     of its citizens.
– Loosely Associated Statements – generally
  related but lack an assertion of proof.
   • Not to value men of worth will keep people from
     contention; not to value goods that are hard to come
     by will keep them from theft; not to display what is
     desirable will keep them from being unsettled of
     mind. (Lao-Tzu, Thoughts from Tao Te Ching)
   Simple Non-Inferential Passages (cont).

– Reports – simple provision of information
   • E.g. A brush fire raging in mountains above Moreno
     Valley, California is threatening a number of homes
     including that of a former dean of the College of
     Arts, Humanities, and Social Sciences.
   • Can serve as premises for an argument, but because
     no supportive linkage is claimed, no argument
           Expository Passages
• Consist of a topic statement, followed by one or
  more sentences that elaborate on or develop the
  topic. If no attempt is made to prove a contention,
  no argument exists.
   – There is a stylized relation of the artist to mass audience
     in sports, especially in baseball. Each player develops a
     style of his own – the swagger as he steps to the plate,
     the unique windup a pitcher has, the clean-swinging
     and hard-driving hits, the precision and grace of infield
     and outfield, the sense of surplus power behind
     whatever is done. (Lerner, America as a Civilization)
              Expository Passages (cont.)

• In some cases expository passages can be treated
  as arguments.
   – Skin and mucus membrane lining the respiratory and
     digestive tracts serve as mechanical barriers to entry by
     microbes. Oil gland secretions contain chemicals that
     weaken or kill bacteria on the skin. The respiratory tract
     is lined by cells that sweep mucus and trapped particles
     up into the throat, where they can be swallowed. The
     stomach has an acid pH, which inhibits the growth of
     many types of bacteria. (Mader, Human Biology)
• A statement on a topic accompanied by one
  or more references to examples of the
  subject phenomenon.
  – At high speeds ordinary objects behave in
    unexpected ways. For example, tornados have
    been know to drive small twigs through homes’
    wood siding.
• A group of statements that shed light on an
  event the existence of which is generally
  agreed upon as a matter of fact.
  – The space shuttle Challenger exploded because
    an O-ring failed in one of the booster rockets.
  – The United States won the battle of Midway
    because the Japanese Navy suffered from
        Conditional Statements
• A statement in the form of “if [antecedent], then
  [consequent]” is not an argument. These may also
  be stated in the form, “[consequent] if
   – If you add water to a bucket it will weigh more than it
     did before.
   – If both Saturn and Uranus have rings, then Saturn has
      • Can the second statement be stated in terms of an argument?
              Conditional Statements (cont.)
• Conditional Statements can be related to arguments, either
  as premises, conclusions, or both.

   – If fast food vendors warn of the dangers of hot coffee, consumers
     assume the risk of burning themselves if they drink coffee while
   – FF vendors put warning labels on coffee cups.
   – Therefore, consumers assume the risk of burns.

   – If power companies make bad investments, they will be threatened
     with bankruptcy.
   – If power companies are threatened with bankruptcy, the taxpayers
     will be forced to bail them out.
   – Therefore, if power companies make bad investments, the
     taxpayers will be forced to bail them out.
             Conditional Statements (cont.)
• Rules for conditional statements
   – A single conditional statement is not an argument
   – A conditional statement may serve as the premise of an argument,
     the conclusion, or both.
   – The inferential content of a conditional statement may be
     reexpressed to form an argument.
      Induction and Deduction
• Deductive – an argument that contains
  premises that are presented in such a way
  that, if the premises are true, the conclusion
  must be true.
• Inductive – a probabilistic style of
  argument. The support provided by the
  premises (if true) makes it likely, but not
  necessary that the conclusion is true.
       Deductive Arguments
• The Matterhorn is higher than Mount
  Whitney and Mount Whitney is higher than
  Mount Rainier. Therefore, the Matterhorn is
  higher than Mount Rainier.
      Types of Deductive Arguments

• Arguments based on mathematics –
   – E.g. a piece of property is measured to be 100 feet wide
     by 200 feet deep. The property contains 20000 square
• Arguments from definitions – arguments based
  simply on the definition of one or more of the
  words in the premise or conclusion.
   – E.g. George is obtuse because he is not terribly bright.
• Syllogisms – a form of argument consisting of two
  premises and one conclusion.
– Three types
   • Categorical – based on a quantification using terms such as
     “all,” “no,” or “some.”
       – All women are short.
       – Elena is a woman
       – Therefore, Elena is short.
   • Hypothetical – a syllogism having a conditional statement as
     one or both premises
       – If quartz scratches glass, then quartz is harder than glass.
       – Quartz scratches glass.
       – Therefore, quartz is harder than glass.
   • Disjunctive – a syllogism that incorporates a disjunctive term
     (an “either” … “or” statement) as a premise.
                   Inductive Arguments

• Predictions – a prediction of some future event based on
  knowledge of past events.
   – E.g. forecasting the weather (see chaos theory)
• Arguments from analogy – a condition affect a known
  thing or situation is applied to a lesser known thing or
  situation because of attributes the two share.
   – Joe’s Pinto is extremely fast. Therefore, Thomas’ Pinto is also fast.
• Inductive generalization – generalizing to a group based on
  knowledge of a sample.
   – See opinion surveys
                        Induction (cont.)

• Argument from authority – argument based on a statement
  or statements made by a authority on the subject.

• Causal inference – arguments that proceed from an
  understanding of cause and effect.
   – If you know that a bottle of water was left in the freezer overnight
     you might conclude that it had frozen.
   – The Case of the Phantom sprinkler.

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