Using Inductive Arguments

1. Using Inductive Arguments

2. Inductive Arguments • Move from specific examples or facts to a general conclusion • Opposite of deduction (syllogisms) • No distinctive form • BUT there is a process to follow

3. Induction - Process • 1) Decide on a question to be answered • Or a tentative answer to a question (hypothesis) • 2) Gather evidence • 3) Move from evidence to conclusion by making an inference

4. Inference • A statement about the unknown based on the known • Answers the question • Takes all evidence into account

5. Inductive process: example (557) • Question: How did that living-room window get broken? • Evidence: • There is a baseball on the living-room floor. • The baseball was not there this morning

6. Inductive process (cont’d) • Evidence: (cont’d) • Some children were playing baseball this afternoon • They were playing in the vacant lot across from the window. • They stopped playing a little while ago. • They aren’t in the vacant lot now.

7. Inductive process (cont’d) • Conclusion: One of the children hit or threw the ball through the window; then, they all ran away.

8. Induction: Problems • One additional piece of evidence can make the conclusion doubtful • Ex: children were playing volleyball, not baseball • Result? True answer can’t be inferred

9. Induction: Problems (cont’d) • Even if conclusion is believable, you can’t necessarily assume it’s true • The window could have broken some other way!

10. Induction: Problems (cont’d) • What if the ball in the living-room had gone unnoticed all day? • The second piece of evidence on the list would be untrue (conclusion is therefore unsound)

11. Induction: Problems (cont’d) • Solution: Consider several possible conclusions • Form multiple hypotheses and test each one • Hypothesis: One of those children playing baseball broke the living room window. • Hypothesis: A bird broke the window.

12. Induction: Problems (cont’d) • If the gap between your evidence and conclusion is too great = jumping to a conclusion • Hasty • Not supported by the facts • Essentially a premature inductive leap

13. Induction: Problems (cont’d) • REMEMBER • Hypothesis is just the starting point! • Continue the inductive process as if the question were still to be answered (which it is)

14. Induction: Problems (cont’d) • More evidence = smaller logical gap between evidence and conclusion • Whatever the size of the gap, the crucial step between evidence and conclusion is called an inductive leap

15. Example of bad inductive leap • Messenger: The Joan of Arc Story • http://www.youtube.com/watch?v=ZtQEXW0lVts

16. Conclusion • Inductive conclusions ARE NOT facts • Facts = verifiable statements • Inductive conclusions are inferences/opinions • Never 100% certain • At best, highly probable

17. Conclusion – Soundness? • Not always easy to move from evidence you’ve collected to sound conclusion • Gap • REPEAT: More information = smaller inductive leap

18. Analysis of “A Scandal in Bohemia” • Sherlock Holmes is a master of deductive reasoning • Irene Adler, “the woman,” beats Holmes using inductive reasoning • What a great twist! Rachel McAdams