2. Sentence (syntactically Independent grammatical unit) QuestionCommandStatement “This is a class in logic.” “I enjoy logic.” “Today is Friday.”

3. Argument Argument is an attempt to persuade someone of something, by giving reasons or evidence for accepting a particular conclusion

4. Premise A premise is a statement that an argument claims will induce or justify a conclusion

5. How to Recognize Arguments?

6. Conclusion Indicators Therefore Hence Thus So Accordingly In consequence Proves that As a result For this reason

7. Premise Indicators Since Because For As Follows from As shown by Inasmuch as

10. Argument Vs Explanation Premise – P Conclusion – Q

11. “Q because P”

12. Validity Validity refers to a relation between propositions.

13. Validity Validity never applies to any single proposition by itself.

14. Validity P -> Q Logical Necessity Deductive/Inductive?

15. Truth & Falsity Truth and Falsity are attributes of individual propositions.

16. Valid Vs True Truth and falsity are attributes of individual propositions or statements, validity and invalidity are attributes of arguments.

17. Valid Arguments, True Propositions All mammals have lungs All whales are mammals Therefore all whales have lungs

18. Valid Arguments, False Propositions All four-legged creatures have wings. All spiders have four legs. Therefore, all spiders have wings.

19. Invalid Arguments, True Propositions If I owned all the gold in Fort Knox, then I would be wealthy. I do not own all the gold in Fort Knox. Therefore, I am not wealthy

20. Invalid Arguments, True Premisses, False Conclusion If Bill Gates owned all the gold in Fort Knox, then Bill Gates would be wealthy. Bill Gates does not own all the gold in Fort Knox. Therefore Bill Gates is not wealthy

21. Valid Arguments, False Premisses, True Conclusion All fishes are mammals. All whales are fishes. Therefore all whales are mammals.

22. Invalid Arguments, False Premisses, True Conclusion All mammals have wings All whales have wings. Therefore, all whales are mammals.

23. Invalid Arguments, False Premisses, False Conclusion All mammals have wings All whales have wings Therefore all mammals are whales

24. Lessons When an argument is valid, and all of its premisses are true, we call it “sound”.

25. Lessons Truth or falsity of an argument’s conclusion does not by itself determine the validity or invalidity of that argument. The fact that an argument is valid does not gurantee the truth of its conclusion. If an argument is valid and its premisses are true, we may be certain that its conclusion is true also. If an argument is valid and its conclusion is false, not all of its premisses can be true.