Sep

25

2009

Justin Taylor|12:00 am CT

A Crash Course in Logic

s-logicSome notes from Peter Kreeft’s Socratic Logic (pp. 28-33):

There are three kinds of thoughts, or three acts of the mind:

  1. Simple apprehension [understanding a simple term--e.g., "man"]
  2. Judging [relating two concepts by predicating one term of the other--e.g., "man is mortal"]
  3. Reasoning [relating two or more judgments with a conclusion--e.g., "man is mortal; I'm a man; therefore I'm mortal"]

These three acts of the mind result in three mental products:

  1. Concepts (the products of conceiving)
  2. Judgments (the products of judging)
  3. Arguments (the products of reasoning, or arguing)

Expressed logically these are:

  1. Terms
  2. Propositions
  3. Arguments (most commonly, syllogisms)

These logical entities answer the three most fundamental questions:

  1. A term answers what something is.
  2. A proposition answers whether something is.
  3. An argument answers why it is.

These logical entities also reveal three aspects of reality:

  1. Terms reveal essences (what something is).
  2. Propositions reveal existence (whether something is).
  3. Arguments reveal causes (why something is).

These logical entities can be judged logically good or logically bad:

  1. Terms are either clear or unclear (=ambiguous).
  2. Propositions are either true or false.
  3. Arguments are either valid or invalid.

To make a convincing argument you have to fulfill all three of the following conditions:

  1. Your terms are clear.
  2. Your premises are true.
  3. Your logic is valid.

If you want to critique someone’s argument, you have to show an error in just one of the following:

  1. They are using a term ambiguously.
  2. They are using a false premise.
  3. They are committing a logical fallacy (i.e., the argument is invalid; the conclusion does not follow from the premises).

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8 Comments

  1. Truth Unites... and Divides
    September 25, 2009 at 12:35 am

    Logical arguments and refutations don’t seem to have much effect when reading Catholic e-pologists, Eastern Orthodox e-pologists, and Conservative Protestant e-pologists going at one another.

    Anyways, I learned two aphorisms this week:

    (A) “Lots of bad arguments gain traction on the basis of good rhetoric.”

    (B) “Attaching deeply-rooted Stigma can whip a good Dogma.”

    Plus I’ve witnessed liberal emotionalism utterly destroy conservative logic in many situations.

  2. Paul
    September 25, 2009 at 8:45 am

    Go Justin!

  3. Pete Scribner
    September 25, 2009 at 8:56 am

    Apparently preachers and long-range jump shooters aren’t the only ones who like three points!

  4. Pastor Jim
    September 25, 2009 at 9:40 am

    Now, if we could only re-interject these concepts into American political discourse….

  5. Brian
    September 25, 2009 at 10:00 am

    Excellent stuff. I think I’ll pick that book up. Thanks.

  6. The Basics of Logic. « BRYANLOPEZ.COM
    September 25, 2009 at 4:25 pm

    [...] HT: JT [...]

  7. Scott Gould
    September 26, 2009 at 7:01 am

    Thank God for the wisdom from above. Else I’d struggle all day making sure the gospel was logical!

Comments are closed.