Apologetics 1 Lesson 6 Tools of Logic


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Lesson 6 of a multipart series. Covering The tools of logic, Three Classic Laws of Thought, Formal Arguments, and Informal fallacies.

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  • Pascal I find your comment interesting. I am not sure how much you know about logic or the historical development of philosophy but almost all the foundational laws of logic were developed by religious people. I would go so far as to say that atheists have contributed little to nothing new on foundational logic. Sure they have debated in philosophy, I grant that, but for the laws of logic, nothing new. So it seems your comment is at best uniformed. This unexamined caricature of religious people is often used to confirm a bias by atheists. Granted there are scores of religious people that certainly do fit the bill, however that does not mean they all are that way. Historically some of the greatest minds in logic and philosophy were religious. I too am frustrated by the shallow intellectualism of many religious people in western society today. They have lost the rich tradition of intellectual rigor that was foundation to western society. So while I appreciate your sentiment of your comment, your comment assumes a logical fallacy that turns back on itself and bite the hand of its owner.
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  • Pretending to teach logic, using it for religious propaganda.... Priceless.
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  • Seeing how this is an introduction, I am not sure more depth would help. Logically we need to start with the simple and work toward the complex.
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  • This lecture in logic is at precisely the level of sophistication I would tend to anticipate from the modern-day Evangelical movement.
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Apologetics 1 Lesson 6 Tools of Logic

  1. 1. Third Column Ministries www.slideshare.net/ThirdColumnMinistries www.facebook.com/LearnApologetics | Twitter: @LApologetics www.ThirdColumnMinistries.org This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License..
  2. 2. Definitions • Epistemology – Theory of knowledge: the branch of philosophy that studies the nature of knowledge, in particular its foundations, scope, and validity. • Logic – Theory of reasoning: the branch of philosophy that deals with the theory of deductive and inductive arguments and aims to distinguish good from bad reasoning. From Bing Dictionary
  3. 3. Logic “Don’t neglect your critical faculties. Remember that God is a rational God, who has made us in His own image. God invites and expects us to explore His double revelation, in nature and Scripture, with the minds He has given us, and to go on in development of a Christian mind to apply His marvelous revealed truth to every aspect of the modern and post-modern world.” – John Stott Logic: “Logic is the study of right reason.… That is the main point. Logic is a study, an ordering, of how to think rightly, or how to find truth. Paraphrasing this, we might say, logic is a way to think so that we come to correct conclusions.” - Geisler and Brooks, Come, Let Us Reason, An Introduction to Logical Thinking p. 13
  4. 4. Is It Futile? • Some people site 1 Corinthians 1-2 to say human reasoning and argumentation are futile. • However, Paul later in the epistle supports argumentation and reasoning. – See 1 Corinthians 15 and examples of Paul in Acts.
  5. 5. 1 Corinthians 1-2 & Colossians 2:8 • “What is in view here is the prideful use of reason not reason itself.” – J. P. Moreland • In addition, Paul’s comments may be directed at the sophists of the time who valued persuasion over logic. – For the sophist it was more important to win a debate than to come to true conclusions.
  6. 6. “Scripture and right reason were considered twin allies to be prized and used be disciples of Jesus.” “Knowledge is the fruit of study, and knowledge is necessary for wisdom.” “The word logos means ‘evidence or argument which provides rational justification for some belief.’” - J. P. Moreland, Love Your God With All Your Mind
  7. 7. Total Depravity • “Some argue that the human intellect is fallen, depraved, darkened, and blinded, and therefore human reason is irrelevant or even suspect when it comes to becoming or growing as a Christian.” - J. P. Moreland • “Total depravity means that the entire person, including the intellect, has been adversely affected by the Fall and is separate from God.” - J. P. Moreland
  8. 8. Total depravity does not mean we should not nor cannot use reasoning skills as anti-intellectuals claim. Total depravity properly understood means that we cannot save ourselves. In Romans 1 Paul tells us we are without excuse because by reason we know there is a God. God has given humans a gift that no other in the animal kingdom has, mainly an intellect, the ability to reason. We are held accountable before God with what reasoning powers we have. It would be a shame, no a sin, to not use the gifts God has given us to their full potential. Our sinful state mares our understanding, it does not eliminate it.
  9. 9. Biblical Faith • Three aspects of Biblical faith – Notitia (knowledge) – Fiducuia (trust) – Assensus (assent)
  10. 10. “God is not honored when His people use bad arguments for what actually may be correct conclusions.” “A confident mind is a mind free to follow the truth wherever it leads, without the distracting fear and anxiety that comes from the attitude that maybe we’re better off not knowing the truth. This is one reason why Christians need not fear the honest examination of their faith.” - J. P. Moreland, Love Your God With All Your Mind
  11. 11. “We can’t avoid reasoning; we can only avoid doing it well.” - Kreeft and Tacelli, Pocket Handbook of Christian Apologetics 9 “Our God is a God of truth, reason and logic.” - Moreland, Love Your God With All Your Mind 113 “Our Lord is a God of reason as well as of revelation.” - Moreland, Love Your God With All Your Mind 43
  12. 12. Definitions • Necessarily false: – Cannot be true in anyway. • Incoherent: – Not clearly expressed or well thought out, and consequently difficult to understand.
  13. 13. Definitions (cont.) • Contradictory: – Statements that are necessarily have opposite meanings or opposite truth values. • Example: – Some people are moral. No people are moral. – Some people cannot be moral if all people are not moral.
  14. 14. Definitions (cont.) • Contrary: – The both cannot be true, at least on is false and both could be false. • Example: – All cars are black. No cars are black. – One must be false they both cannot be true but they both could be false as in this example.
  15. 15. Definitions (cont.) • Converse: – Switching the subject and the predicate. • Example: – All Fords are cars. All cars are Fords. – Some Fords are cars. Some cars are Fords.
  16. 16. Law of Identity • It states that an object is the same as itself: A → A (if you have A, then you have A). – “This illustration can be generalized into a truth about the nature of identity: For any x and y, if x and y are identical (they are really the same thing, there is only one thing you are talking about, not two), then any truth that applies to x will applies to x will apply to y and vice versa. This suggests a test for identity: if you could find one thing true of x not true of y, or vice versa, then x cannot be identical to (be the same thing as) y.” J.P. Moreland
  17. 17. Law of Noncontradiction • Self-refutation is a statement that cannot satisfy its own standard. • The statement refers to itself and fails to satisfy its own criteria. • Ask yourself, “Does the claim apply to itself?” • Examples: – “All English sentences are false.” – “There is no truth.” – “There are no absolutes.” – “I do not exist.”
  18. 18. Law of Excluded Middle • It states that for any proposition, either that proposition is true, or its negation is. • Example: – Socrates is mortal. – Mortality has only two states, mortal or immortal. – There is no state of partial mortality (no middle ground). – Either Socrates is mortal, or it is not the case that Socrates is mortal.
  19. 19. Arguments • Premise, a proposition that forms the basis of an argument or from which a conclusion is drawn (Encarta World English Dictionary). • Conclusion, a decision made or an opinion formed after considering the relevant facts or evidence (Encarta World English Dictionary).
  20. 20. Types • Deductive arguments are either valid or invalid. If the premises are true it follows the conclusion must be true. A valid argument is a sound argument. • Inductive arguments don’t guarantee that the premises validate the conclusion, however they supply support for the conclusion. – Probability not certainty. – Facts are determined by repeated observations.
  21. 21. Syllogisms • A syllogism is a deductive argument that consists of exactly two premises and a conclusion. • Example: – Major premise: All mammals are warm-blooded. – Minor premise: All black dogs are mammals. – Conclusion: Therefore, all black dogs are warm- blooded.
  22. 22. Polysyllogism • A string of any number of propositions forming together a sequence of syllogisms such that the conclusion of each syllogism, together with the next proposition, is a premise for the next, and so on. • Example: – It is raining. – If we go out while it is raining we will get wet. – If we get wet, we will get cold. – Therefore, if we go out we will get cold.
  23. 23. Valid • The validity of an argument does not depend on the actual truth or falsity of its premises and conclusions. • The validity of an argument depends solely on whether or not the argument has a valid logical form.
  24. 24. Sound • A sound argument is a valid argument with true premises. • A sound argument, being both valid and having true premises, must have a true conclusion.
  25. 25. Burden of Proof • What level of proof is sought? – Absolute certainty – Beyond reasonable doubt – Preponderance of evidence – Clear and convincing – Compelling – Probable • Something is certain only if no skepticism can occur.
  26. 26. Burden of Proof • Semper necessitas probandi incumbit ei qui agit. • The necessity of proof always lies with the person who lays charges.
  27. 27. Evaluating Evidence and Claims • Three Questions: – Is it possible? Is it even remotely possible? – Is it plausible? Is it logically consistent? Is it reasonable? – Is it probable? Is it the best explanation given all the evidence?
  28. 28. “…examining [arguments] can help us to see how subtle but misleading arguments can be untwisted through careful reading and good thinking.” - James Sire “You follow the evidence of what you can see to conclude the existence of something you cannot see. The effect needs a cause adequate to explain it.” - Greg Koukl “…when we use our reason and base our decisions on the best assessment of the evidence we can make, we increase our chances that our decisions are based on true beliefs.” J. P. Moreland “Taking the roof off” assume for the sake of argument their idea or premise then take that premise and put it to the practical test and see where it goes. “It forces people to ask if they can really live with the kind of world they are affirming.” - Greg Koukl
  29. 29. Informal Fallacies • An informal fallacy is an argument whose stated premises fail to support their proposed conclusion. • The deviation in an informal fallacy often stems from a flaw in the path of reasoning that links the premises to the conclusion. – http://en.wikipedia.org/wiki/Informal_fallacy
  30. 30. Informal Fallacies • Informal fallacies do not necessarily mean the conclusions are false. • They mean the logic used to arrive at the conclusion is faulty. • Using informal fallacies in arguments weakens our credibility and the credibility of our claims.
  31. 31. “Remember, a fallacious argument may or may not have a true conclusion. Either way, such an argument fails to establish that conclusion properly.” - J.P. Moreland “We can meet [fallacies] in two ways: (1) when we use them unwittingly and get caught by our audience and (2) when our dialogue partners spring them on us as objections to our argument. In both cases we need to keep our wits about us, admit when we’ve been unfair and be gentle when we point out the errors of others.” - James Sire
  32. 32. Logical Fallacies Accident Begging the Question False dilemma Ad Hominem Abusive ad hominem Appeal to hypocrisy Appeal to the masses Association to Hitler Appeal to force Amphiboly Post Hoc Poisoning the Well Slippery Slope Single Cause Hypothesis Contrary to Fact Fallacy of Association Appeal to Tradition Appeal to authority Appeal to pity Genetic Fallacy Red Herring Straw Man Distribution Fallacy Appeal to ignorance Equivocation Gambler's Fallacy Appeal to emotion Special Pleading Hasty generalization False Analogy And many more…