1: A never works alone
∴ 2: If A was involved, then somebody else was involved (from 1)
3: We have narrowed it down to three suspects: A, B, and C
∴ 4: Nobody other than A or B or C was involved (from 3)
(5) If A was involved then B or C was involved. (6) C refuses to work with A ∴ (7) If A was involved C was not involved ∴ (8) If A was involved, then B was involved. (9) C always uses an accomplice ∴ (10) If C was involved, then someone else was involved. ∴ (11) If C was involved, then either A or B was involved. (12) If C was involved then A was not involved. ∴ (13) If C was involved, then B was involved (11 and 12) (14) If B was involved, then B was involved (SP) (15) If either A, B, or C was involved, then B was involved (8, 13, 14) (16) “At least one of them was involved.” ∴ (17) B was involved. (from 15 and 16)
Mystery 2 (homework) 1. “Everyone at Royston North High wears monogrammed jackets.”
2. “The Hawks all go to Royston North High.”
∴ (3) All Hawks wear monogrammed jackets.
4. “No one who eats at Joe’s wears a monogrammed jacket.”
∴ (5) No Hawk eats at Joe’s. (from 3 and 4)
6. “Only those who eat at Joe’s collect green matchbooks.”
∴ (7) No Hawk collects green matchbooks. (from 5 and 6)
8. “Everyone who hangs out on Laraby Street collects green matchbooks.”
∴ (9) No Hawk hangs out on Laraby Street. (from 7 and 8)
10. “Only kids who hang out on Laraby Street fight on weekdays.”
∴ 11. No Hawk fights on weekdays. (from 9 and 10)
12. Everyday before Saturday is a weekday. (suppressed premise)
∴ (13) Anyone who fights before Saturday fights on a weekday.
∴ (14) No Hawk fights before Saturday. (from 11 and 12)
15. If no Hawk fights before Saturday, then those gangs won’t get together to fight until at least Saturday. (SP)
∴ (16) “Those gangs won’t get together to fight until at least Saturday.” (from14 and 15)
Hoodie or Racism? “The hoodie killed Trayvon Martin as surely as George Zimmerman.” – Geraldo Riviera
George Zimmerman Trayvon Martin
TPHIL 250 Winter 2019
Week 5, February 7
Inductive and Deductive Arguments
Deductive: Conclusion necessarily follows from the truth of the premises.
Inductive: Infers probable and likely conclusions. The conclusion does not necessarily follow from the premises.
Deductive and Inductive
• Premise of a good deductive argument if true, demonstrates that the conclusion is true.
Bill Clinton is taller than GW Bush and Jimmy Carter is shorter than GW Bush. Therefore, Clinton is taller than Carter.
• Premise of a good inductive argument does not demonstrate its conclusion, it supports it.
Alex rarely returns texts. Therefore, she probably rarely returns emails.
Deductive and Inductive 1. Every human being has rights. John is a human being.
Therefore, John has rights. – Valid due to form – True by definition
– Proof not evidence
– Premises provide conclusive support for conclusion
2. Six to ten children who are allowed to drink at home with their parents become alcoholics later in their lives. Therefore, attitudes towards drinking are likely to be formed by others near to us.
1. Almost all of the students at this school are Democrats.
2. Therefore, Maria, who is a student here, is probably a Democrat too.
1. 90 percent of the Republicans I know are Volvo owners.
2. Therefore, 90 percent of all Republicans are probably Volvo owners.
Source: Vaughn, Writing Philosophy
“The Ultimate Computer”- Star Trek TOS
Are androids/cyborgs life forms with rights?
Homework #5 to be submitted in class on Tuesday 2-12-2019 • Star Trek TOS “The Ultimate Computer”: Work out a deductive or an
inductive argument based on the issue of whether the M-5 can replace the crew of the Enterprise.
• Star Trek TNG “The Quality of Life”: Work out an inductive argument on whether the Exocomps are life forms with rights as given by Data in Star Trek TNG “The Quality of Life”. Test if the argument is strong or weak and if so, test if its cogent or not. Please use reconstruction methods as learnt in chapter 5.