A very simple introduction to logic designed for my high school senior writing students who were failing to make logical connections.

1. Logic
This Web site provides, through a range of materials and tools, an introduction to the
study of elementary logic covering propositional and predicate calculus. It is aimed
especially at first year undergraduates studying Philosophy at the University of
Oxford, but it is hoped that the site may be useful more widely, for anyone who
would like to investigate the subject.
"Elementary, my dear
Watson."
Unless otherwise noted all content comes from: http://logic.philosophy.ox.ac.uk/

2. Consistent
Inconsistent
(
Not contradictory
Contradictory
)
 Peter believes that Mary is a woman and that she has
three hundred children.
 Peter believes that David has three daughters and four
sons, and Davidhas six children in all.
 Peter believes that David has exactly four children, that
David'ssister is Mary and that Mary's only brother has
three children.
 Men have children. Peter is a man. Peter has children.
 Men have children. Peter is a man. Peter does not have
children.

3. Lexical
Ambiguity
Structural
Ambiguity
Lexical
 "You know, somebody
actually complimented me
on my driving today. They
left a little note on the
windscreen; it said, 'Parking
Fine." So that was nice."
 "Outside of a dog, a book is
a man's best friend; inside
it's too hard to read."
 The Rabbi married my sister.
 She is looking for a match.
Structural
 The professor said on
Monday he would give an
exam.
 The chicken is ready to eat.
 Visiting relatives can be
boring.
 The burglar threatened the
student with a knife
http://grammar.about.com/od/il/g/lexicalambiguityterm.htm http://grammar.about.com/od/rs/g/syntacticambiguityterm.htm

4. Arguments
An argument consists of a conclusion (which is what is being argued for) and
a premise or premises which are the considerations which are being offered in
favour of the conclusion.
For example:
Socrates is a man. All men are mortal. So, Socrates is mortal.
The premises of this argument are, of course, "Socrates is a man" and "All men are
mortal" and the conclusion is "Socrates is mortal".
Note: the conclusion of an argument need not come at the end. It might come at the
beginning, as in:
Socrates is mortal. For all men are mortal, and he is a man.
Or in the middle, as in:
Socrates is a man. So, he is mortal. For all men are mortal.

5. Arguments
1. John will come to the party, because he has been invited, and he likes parties.
2. John doesn't like parties. So he will come to the party because he has been
invited. For he always accepts invitations.
3. Mary says that Manchester United will beat Derby County. So , since she is
always right about such things, they will.
4. Mary says that Manchester United will beat Derby County. So, if she is right
about such things, they will.
Identify the premises (2)
and conclusion (1).

6. Validity
 An argument is valid just if it would be impossible for its
premises all to be true and its conclusion false simultaneously.
 In a valid argument, there is no need for the premises to be
true. (One may want the premises of one's argument to be true;
but their not being true does not affect itsvalidity.
 All dogs go to Heaven. Dingo is a dog. Dingo will go to Heaven.
 All people are dumb. Sam is a person. Sam is smart.

7. Validity
 Either The Patriots or the Philadelphia Eagles will win the Superbowl.
The Patriots lost.
Therefore The Eagles won.
 Michael J Fox has Parkinson's disease.
Michael J Fox is a vegetarian.
To be healthy one should eat meat.
http://kslinker.com/VALID-AND-INVALID-ARGUMENTS.html