Eric Douma: A Primer in Logic – Echo Zoe Ministries

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In coming months, Echo Zoe Ministries will be presenting a seminar on Logic. My guest this month, Eric Douma, and I will be teaching hour-long sessions over several weeks after church. I will be teaching informal logical fallacies, and Eric will be teaching formal logic. This episode is a primer of what is to come. In this episode, I present six of the most common logical fallacies that we encounter in our daily lives, and Eric gives a very basic introduction of the Laws of Formal Logic and a few formal principles in logic. He also explains why logic is necessary, and how logic fits in with our understanding of Scripture.

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An Outline of the Discussion

Logic is important. It's not just an invention of Aristotle, but rather an expression of General Revelation. It describes rational thought.
Logic helps us to make our understanding of the world and the Scriptures cogent, and also helps us spot errors.
If a logical argument is formed correctly, and the premises are true, the conclusion must necessarily be true.
Paul uses formal logic in the form of a HypotheticalÂ SyllogismÂ in 1 Corinthians 15:13, saying “But if there is no resurrection of the dead, not even Christ has been raised”

Informal Logical Fallacies:

AnÂ Ad HominemÂ (against the man) is a fallacy that seeks to discredit an opponent's point and argument by attacking the person, rather than the argument he's making. In the clip we played of the Piers Morgan Show, Suze Orman attacks a proponent of traditional marriage by calling him “really, really uneducated in how it works.” Calling him “uneducated” does not address his argument for the traditional/natural definition of marriage, and is irrelevant to the discussion.
In anÂ Appeal to Emotion, seeks to win people over by conjuring up emotions. It is a form of Red Herring fallacy because it distracts from the real issue (much the same way the previously mentioned Ad Hominem fallacy does.) In the clip we played of the same Piers Morgan episode, Morgan paints an emotionally loaded image of Suze Orman in order to attack the gentleman who is not in favor of changing the definition of marriage to suit her current relationship with her lesbian partner. The fact that Orman is successful, or that she's a nice person, is irrelevant to the discussion of whether or not to redefine marriage.
TheÂ Bandwagon, orÂ Appeal to the People, is a fallacy that seeks to win the argument solely on the grounds of popularity.Bandwagon and Appeal to the People is sometimes presented as the same fallacy, and sometimes divided into two separateÂ fallacies. Those who separate them will say that Bandwagon appeals to popularity as evidence of quality (seeks to shape opinion), whereas Appeal to the People appeals to popularity as evidence of authority (seeks to prove a fact). The difference is subtle enough that I can see either option (separating them or considering them the same) as reasonable.
Piers Morgan commits this fallacy by appealing to the shift in polls on same-sex “marriage” as evidence that marriage should be redefined.
Appeal to AuthorityÂ is a fallacy in which a premise is used that relies on an authoritative source that is not actually authoritative in the subject of the debate. In the clip we played of Piers Morgan discussing gun control, Morgan appeals to General Stanley McChrystal, who states that his knowledge of the destructive power of military rifles leads him to oppose civilian ownership of similar weapons. This is fallacious because McChrystal is not an authority on the legal arguments of gun ownership, but rather of the physical characteristics of specific firearms. It is another Red Herring argument.
AÂ Straw ManÂ is an argument that creates a false presentation of an opposing view, either by distortion orÂ exaggeration, that is easier to discredit than the actual view of the opponent. Piers MorganÂ erectsÂ a Straw Man of Larry Pratt's view on guns by stating that Pratt wants every school, hospital, or other public place to be filled with people who are armed. Pratt likely believes that people in those places have the right and should be legally entitled to be armed, but to state that they must have armed people in them would be a misrepresentation of his actual view by means ofÂ exaggeration.
AÂ Genetic FallacyÂ is a form of Ad Hominem and Red Herring argument that attacks an argument as being invalid simply because it's held by a person with unfavorable characteristics or behavior. The characteristics or behavior are irrelevant to the discussion. In the example we discussed, Eric had attacked the view of RC Sproul Jr on the issue of preaching style on the grounds that Sproul is holds an ammillenial view of eschatology, which is irrelevant to the topic of preaching style.
As a “Bonus” fallacy, we discussedÂ Reductio ad Hitlerum, which is also known as “The Nazi Card.” It seeks to discredit a person's view as being shared with Adolf Hitler and/or the German Nazi Party. A counterpart that we face within Christendom is “The Pharisee Card.” Agreeing with Hitler or the Pharisees on a particular point (such as dog ownership in the case of Hitler, or hand washing in the case of the Pharisees) does not make a person or his argument necessarily wrong.

Formal Logic:

The Laws of Formal Logic:
- The Law of Non-Contradiction
- The Law of Identity
- The Law of Excluded Middle
- The Law of Rational Identity
Post-Modernism, which dominates our culture today, holds the view that we don't have access to truth. They deny the laws of logic, and call themselves “post-foundationalists.”
The Law of Non-Contradiction states that A cannot be Non-A at the same time and in the same relationship.
One must use the Law of Non-ContradictionÂ to deny theÂ Law of Non-Contradiction. Eric quotes Norm Geisler, who says that if you must assert something to be true in order to deny that it exists, you don't have a very good case. Greg Koukl of Stand to Reason refers to this as an argument that commits suicide, and addressing it as such is “the suicide tactic.”
The Law of Identity says that something is itself: a chair is a chair, a book is a book, etc.
The Law of Excluded Middle is used when something is either A or B, and cannot be anything else. For example, an unborn child is either a human being, or not a human being, there is no other option.
Formal logic uses Deductive or Inductive Reasoning.
Deductive reasoning usesÂ a prioriÂ arguments, which is to say that something is necessarily true.
Inductive reasoning yeilds conclusions that are probably. Causes are determined from effects (reverse of deductive reasoning).
Deductive reasoning usesÂ syllogisms, which are arguments that have two premises and a conclusion.
If an argument is formed in a formally valid manner, and the premises are true, the conclusion must necessarily be true. The example I gave is this:
- My son's toy is a ball.
- All balls are round
- Therefore, my son's toy is round.
In valid form, two affirmative premises cannot lead to a negative conclusion. The example given was an invalid argument used by the Arians of the 4th century, which stated:
- All members of the Trinity are all fully God (affirmative)
- The other members of the Trinity take orders from God the FatherÂ (affirmative)
- Therefore, the other members of the Trinity are not equal to God the Father (negative)
Informal Fallacies address situations where arguments are validly formed according the laws of Formal Logic, but the conclusion does not necessarily follow the premise.
A sound argument has valid form and premises that are true.
Different forms of syllogisms: categorical, disjunctive, or conjunctive.
A categorical syllogism is an if/then argument (if there are noÂ resurrections, then Jesus was not resurrected.)
A disjunctive syllogism is an either/or argument (if man was created, then he did not evolve from apes.)
AÂ conjunctiveÂ syllogism is a both/and argument (Jesus is fully God and fully man)
Another argument of Formal Logic is theÂ Dilemma,Â which leverages the Law of Excluded Middle. For example, in the atheistic worldview, the universe is either eternal or it is not. If it is eternal, it has always existed, thus violating the 2nd law of thermodynamics (the universe will eventually succumb to heat death). If the universe is not eternal, it had a beginning, it would have had to have created itself. The Law of Non-Contradiction states that it can't have both existed in order to have created itself, and not existed (necessitating it's creation) at the same time.