Evaluating Philosophical Claims and Theories

Argument?

Obama is not trustworthy.

Abortion should be made illegal in all cases except when a woman’s life is endangered by continuing the pregnancy. Additionally, doctors who perform abortions should be charged with murder.

If Americans want to continue to be competitive in the global economy, then they need to decrease military spending and increase funding for public education.

CR’s main campus is located at the southern end of Eureka.

It is irrational to believe that human spirits or souls exist because there is no evidence that justifies this belief.

Argument

“An argument is a set of statements in which one or more of the statements attempts to provide reasons or evidence of the truth of another statement” (40).

• Premise.• Conclusion.• Inference.

It is irrational to believe that human spirits or souls exist because there is no evidence that justifies this belief.

Analyzing an Argument1. Identify premise(s) and

conclusion.

2. Arrange the argument so that the conclusion appears after the premise(s).

It is irrational to believe that human spirits or souls exist because there is no evidence that justifies this belief.

There is no evidence that justifies the belief that human spirits and souls exist.

Therefore, it is irrational to believe that human spirits or souls exist.

3. Determine whether the argument depends on any unstated premises and, if so, add to these to the argument.

4. Determine whether the argument is deductive or inductive.

5. Deductive: determine whether the argument is valid.

6. Deductive: determine whether the argument is sound.

It is irrational to believe that something exists if there is no evidence that justifies the belief.

There is no evidence that justifies the belief that human spirits and souls exist.

Therefore, it is irrational to believe that human spirits or souls exist.

It is irrational to believe that something exists if there is no evidence that justifies the belief.

There is no evidence that justifies the belief that human spirits and souls exist.

Therefore, it is irrational to believe that human spirits or souls exist.

• Conceptual Clarity.

It is irrational to believe that something exists if there is no evidence that justifies the belief.

There is no evidence that justifies the belief that human spirits and souls exist.

Therefore, it is irrational to believe that human spirits or souls exist.

It is irrational to believe that something exists if there is no evidence that justifies the belief.

There is no evidence that justifies the belief that human spirits and souls exist.

Therefore, it is irrational to believe that human spirits or souls exist.

• Logical Inconsistency.

• Self-Referential Inconsistency.

• Coherence.

• Comprehensiveness.

• Compatibility.

“Philosophy is not simply the sharing of personal opinions…The goal of philosophical reflection is

not simply to have emotionally satisfying beliefs, but the goal is to have beliefs that are true” (45).

Evaluate: “The truth or falsity of a belief is determined by the person holding the belief because there is no objective truth, only subjective truth. Therefore, what is true to one person may be false to another person.”

“Evaluating philosophies is not like tasting foods” (37).

If the universe exhibits qualities of design, the universe had a designer.

The universe exhibits qualities of design.

Therefore, the universe had a designer.

Modus PollensIf P, then Q.P.Therefore, Q.

If the universe exhibits qualities of design, the universe had a designer.

The universe had a designer.

Therefore, the universe exhibits qualities of design.

Affirming the Consequent (Invalid)If P, then Q.Q.Therefore, P.

If the government imposes import restrictions, the price of automobiles will rise. Therefore, since the government will not impose import restrictions, it follows that the price of automobiles will not rise.

Identify conclusion and premise(s) and arrange for analysis.

If the government imposes import restrictions, the price of automobiles will rise.

The government will not impose import restrictions.

Therefore, it follows that the price of automobiles will not rise.

Valid?

Denying the Antecedent (Invalid)If P, then Q.Not-P.Therefore, not-Q.

Using Counterexamples to Demonstrate Invalidity (but not validity)

If the government imposes import restrictions (P), then the price of automobiles will rise (Q).

The government will not impose import restrictions (not-P).

Therefore, it follows that the price of automobiles will not rise (not-Q).

Denying the Antecedent (Invalid)If P, then Q.Not-P.Therefore, not-Q.

If Abraham Lincoln committed suicide (P), then Abraham Lincoln is dead (Q).

Abraham Lincoln did not commit suicide (not-P).

Therefore, Abraham Lincoln is not dead (not-Q).

If human rights are recognized, then civilization flourishes. If equality prevails, then civilization flourishes. Therefore, if human rights are recognized, then equality prevails.

Valid?True premises?

Counterfeit Hypothetical Syllogism (invalid)If P, then Q.If R, then Q.Therefore, if P, then R.

Verify by Counterexample

If the air conditioner is running, then there is a supply of electricity to the house.

If the heater is running, then there is a supply of electricity to the house.

Therefore, if the air conditioner is running, then the heater is running.

If human rights are recognized (P), then equality prevails (Q).

If equality prevails (Q), then civilization flourishes (R).

Therefore, if human rights are recognized (P), then civilization flourishes (R).

Hypothetical Syllogism (Valid)If P, then Q.If Q, then R.Therefore, if P, then R.

Either people are born with their fundamental personality characteristics or people develop their fundamental personality characteristics through their experiences of their environment. I believe people develop their fundamental personality characteristics through their experiences of their environment. Therefore, people are not born with their fundamental personality characteristics.

InvalidEither P or Q.Q.Therefore, not-P.

Either people are born with their fundamental personality characteristics or people develop their fundamental personality characteristics through their experiences of their environment. I believe people do not develop their fundamental personality characteristics through their experiences of their environment. Therefore, people are born with their fundamental personality characteristics.

ValidEither P or Q.Not-Q.Therefore, P.

Remember the process….

1. Identify premise(s) and conclusion.

2. Arrange the argument so that the conclusion appears after the premise(s).

3. Determine whether the argument depends on any unstated premises and, if so, add to these to the argument.

4. Determine whether the argument is valid.

5. Determine whether the argument is sound.

6. Check for

• Conceptual Clarity.

• Consistency (Logical Inconsistency & Self-Referential Inconsistency).

• Coherence.

• Comprehensiveness.

• Compatibility.

If College of the Redwoods fails to improve the quality of instruction, then it is likely that CR will lose students to

other California Community Colleges in the years ahead.

• Not an argument.

It looks to me like College of the Redwoods is closed today and not holding classes. Jerry said last night that if it is snowing when we wake up in the morning, then College of the Redwoods will be closed and will cancel classes, and sure enough, when I woke up

this morning, it was snowing.

If it is snowing, CR is closed and not holding classes.

It is snowing.

CR is closed and not holding classes.

Modus Ponens (affirming the antecedent): Valid

If P, then Q.P.Therefore, Q.

It looks to me like College of the Redwoods is open today and holding classes. Jerry said last night that if it is snowing when we wake up in the morning, then College of the

Redwoods will be closed and will cancel classes, but when I woke up this morning, it was not snowing.

If it is snowing, CR is closed and not holding classes.

It is not snowing.

CR is open and holding classes.

Denying the Antecedent: Invalid

If P, then Q.Not-P.Therefore, not-Q.

It must be snowing outside today. Jerry said last night that if it is snowing when we wake up in the morning, then College of the

Redwoods will be closed and will cancel classes, and when I woke up this morning I got a text from CR saying that campus is

closed and classes are cancelled.

If it is snowing, CR is closed and not holding classes.

CR is closed and not holding classes.

Therefore, it is snowing.

Affirming the Consequent: Invalid

If P, then Q.Q.Therefore, P.

It must not be snowing outside today. Jerry said last night that if it is snowing when we wake up in the morning, then College of the Redwoods will be closed and will cancel classes, and when I woke up this morning I got a text from CR saying that campus is

open and classes are being held.

If it is snowing, CR is closed and not holding classes.

CR is open and holding classes.

Therefore, it is not snowing.

Modus Tollens (denying the consequent): Valid

If P, then Q.Not-Q.Therefore, not-P.

Human beings experience themselves as more than just a material being of flesh, blood, bone, and electro-chemical events. If human beings possess a non-material self or soul, then human beings will experience themselves as more than just a material being of flesh, blood, bone, and

electro-chemical events. Therefore, human beings possess a non-material self or soul.

If human beings possess a non-material self or soul (P), then human beings will experience themselves as more than just a material being of flesh, blood, bone, and electro-chemical events (Q).

Human beings do experience themselves as more than just a material being of flesh, blood, bone, and electro-chemical events (Q).

Therefore, human beings possess a non-material self or soul (P).

Prove invalid by counterexample?

• If human beings have the ability to inhabit two different spatial locations at one time, then human beings will know what is happening in two places at the same moment.

• Human beings know what is happening in two places at the same moment.

• Therefore, human beings have the ability to inhabit two different spatial locations at one time.

Since the good, according to Plato, is that which furthers a person’s real interest, it follows that in any given case when the good is known, men will seek it.

(from Philosophy and the Human Spirit by Avrum Stroll and Richard Popkin).

If the good is that which furthers men’s real interest, men will seek it when it is known.

The good is that which furthers men’s real interest.

Therefore, in any given case when the good is known, men will seek it.

• Valid.

• Conceptual Clarity.

• Consistency (Logical Inconsistency & Self-Referential Inconsistency).

• Coherence.

• Comprehensiveness.

• Compatibility.

To every existing thing God wills some good. Hence, since to love any thing is nothing else than to will good to that thing, it is manifest that God loves every

thing that exists. (from Summa Theologica by Thomas Acquinas)

If God wills some good to every existing thing, then God loves every existing thing.

God wills some good to every existing thing.

Therefore, God loves every thing that exists.

• Valid.

• Conceptual Clarity.

• Consistency (Logical Inconsistency & Self-Referential Inconsistency).

• Coherence.

• Comprehensiveness.

• Compatibility.

Arguments and StatementsThe City of Eureka should clear out the area behind the Bayshore Mall and destroy all the homeless encampments.

The Bayshore Mall is a fantastic shopping venue because it offers great prices and a diversity of stores.

Go to the Bayshore Mall and buy some food at Pretzel Wetzel.

Is there a Pretzel Wetzel at the Bayshore Mall?

The homeless living behind the Bayshore Mall are responsible for a wide variety of property crimes and cause significant environmental damage. They should be forcibly removed.

Even though the common perception is that property crimes have increased recently in Humboldt County, in fact, they have actually decreased.

Validity

Either she’s running late or she ditched me to hang out with someone else.

She’s running late.

Therefore, she didn’t ditch me to hang out with someone else.

Either she’s running late or she ditched me to hang out with someone else.

She’s not running late.

Therefore, she’s ditched me to hang out with someone else.

Valid?

If I am alive, then I am breathing.

I am breathing.

Therefore, I am alive.

If I am disliked by my friends, then I won’t be invited to their party.

I wasn’t invited to their party.

Therefore, I am disliked by my friends.

Valid

If it is Saturday, then the school will be closed.

The school is closed.

Therefore, it is Saturday.

If it is Saturday, then the school will be closed.

It is Saturday.

Therefore, the school will be closed.

Valid?

If today is February 14, then today is Valentine’s Day.

Today is not February 14.

Therefore, today is not Valentine’s Day.

If Jack was born, Jack will die.

Jack won’t die.

Therefore, Jack wasn’t born.