Argument

1
Argument

• Premises
• Conclusion

2
Conclusion Indicators

• Thus
• Therefore
• Hence
• This shows that
• This suggests that

• Consequently
• So
• Accordingly
• This implies that
• This proves that

3
Premise Indicators

• Since
• Because
• For
• In view of
• This is implied by

4
Arguments

• Good Justifies acceptance of the conclusion
• Valid If the premises are true, the conclusion
  must be true
• Sound All premises are true
• Strong Unlikely that if the premises are true
  the conclusion is false

5
Arguments,

• Deductive An argument that is either valid or
  intended by its author to be so.
• Inductive An invalid argument whose premises are
  intended to provide some support, but less than
  conclusive support, for the conclusion.

6
Deductive Reasoning

• Generally described as moving from general
  principles to particular phenomena.
• In a simple-minded example, knowing the existence
  of gravity makes one able to predict the likely
  direction of movement of any unsupported object
  in a gravitational field.
• In a practical (but related) example, having
  observed the direction of movement of a number of
  unsupported objects on the surface of the Earth
  makes it easy to predict the movement of any
  other unsupported objects under similar
  conditions (things fall down--a thing will fall
  down when dropped).
• Knowing that public buildings contain, among
  other things, drinking fountains and telephone
  booths (general principles) one may confidently
  expect to satisfy the need for such amenities
  based on the likely prediction of finding either
  in a given building (a particular phenomenon).

7
Examples of Deductive Reasoning

• Deductive reasoning (or deduction) is the way in
  which the human adult survives.
• We do not walk into a public street without
  looking for cars any more than one of our
  prehistoric ancestors would walk into the den of
  a cave bear without checking for occupancy.
• We match our immediate experience with our armory
  of general principles about the way the world
  works and satisfy ourselves that we are in no
  danger.
• We also use this technique to find the resources
  needed to keep us alive. Having general ideas
  about where food is found (whether in a tree or
  in a market) enables the prediction of its
  specific locations thereby helping to ensure
  survival.

8
Inductive Reasoning

• Generally described as moving from particulars to
  general principles.
• How many times do we find food under a certain
  kind of rock or in a certain type of tree before
  we begin to realize that food ought to be sought
  there?
• The generalizations that food can be found under
  white rocks or in slender trees with peeling bark
  are derived by inductive reasoning.
• Induction is the natural work of a small child
  ("You can't teach an old dog new tricks.").
• An important function of a complex environment is
  to provide the child with experiences needed to
  induce the generalizations required for a
  successful life.
• Knowledgeable parents gauge toys and experiences
  to the developmental level and temperament of the
  child. It is the constant knowledge and fear that
  induction is yet imperfect that leads parents to
  restrict the explorations of young children to
  "safe" activities ("Be home before midnight!")
• Bad judgment can lead to survival failure.

9
More Inductive Reasoning

• Deduction, then, is the reward of induction.
• As we mature, we gain the ability to filter our
  perceptions and experiences through a complex web
  of conventional, induced notions about the causes
  and consequences of a vast array of daily
  phenomena.
• We use the predictions made by deductive
  reasoning for countless small decisions in the
  conduct of our lives.
• "Is it safe to cross the street?" "Is that noise
  in the basement the cat or an intruder?" "How
  will my boss respond to my request for a leave
  day?" "Will this log across the stream support my
  weight?" "Will I be able to stop the car in
  time?"
• All such questions are best answered by deduction
  based on existing, induced principles. In other
  words, by using good judgment.
• In a "natural" human habitat induction is
  practiced mainly by children. It is the rare
  adult who discovers something truly new (they are
  content with what they learnt).
• The ability that children have to look at
  ordinary things in fresh ways leads us to remark
  about the "innocence of children" and the "joy of
  simple discovery" characteristic of the way a
  child looks at the (mundane, dirty old) world.
• Unfortunately, this inquisitive inductive phase
  of human development is usually cut short by
  imposed educational philosophies which, by
  turning the favored generalizations of
  high-ranking educators into dogma, stifle
  creative exploration.