Faith & Reason - Logical fallacies, definitions, deductive reasoning, and inductive reasoning

amphiboly

deception or confusion when words become ambiguous because the grammatical structure lets them be interpreted in more than one way.

ex. “Her husband gave her cat food.” Could mean the husband gave the wife’s cat food to eat or he gave his wife cat food for her to consume.

equivocation

Confusion or deception because the same word has more than one meaning.

ex. “Remember in prayer the many who are sick of our church and community” Sick of can mean physically ill or repulsed by.

Argument to the man (ad Hominem)

could be called “personal attack” or “name calling.” Denigrating the qualities, skills, or character of a person to distract the listener from the merits of what he is saying.

ex. “You don’t know anything about relationships. You are just a teenager.”

Poisoning the Well

denigrating the person before he has had a chance to speak, so that no one will take his argument seriously. Done preemptively.

ex. The pope is a celibate old man. Keep that in mind when he says things about sex before marriage.

Appeal to Mercy

a way of distracting people from the reasonable demands of what is right, moral, and just. This is an abuse of mercy and pity.

ex. “This man is suffering so much. Why can’t you let him ask for a lethal injection to end his pain?” The degree of suffering does not resolve the serious question of whether it is ever ethical to kill an innocent person.

Appeal to Shame

Going against the one(s) in authority which would make you feel ashamed. Also called appeal to authority as it deals with peer pressure.

ex. “All the educated people agree that Jesus never really rose from the dead. You seriously think he did?” Speaker tries to make you ashamed of not being one of the “educated people.”

tu quoque

defending your ideas or behavior by accusing the person who is criticizing you of doing the same thing, that is, of being a hypocrite. It diverts attention away from the behavior in question by shaming the person doing the intervention. This person may have gained wisdom from past mistakes and is trying to help someone else not to repeat them. Latin for “you too.”

ex. “You can’t tell me not to vape. You used to smoke.”

Appeal to the stick

Using physical, psychological, or moral threats to compel agreement.

ex. “When the boss asks how things are going in our office, you will tell him that everything is perfect, if you know what’s good for you.”

Appeal to a Red Herring

an irrelevant point or argument, introduced in order to divert attention from the real issue.

ex. Father: “Why did you come home past your curfew?” Daughter: “You always hated my boyfriend?”

Begging the question

The speaker assumes what he is trying to prove. Sometimes called a “circular argument.” Words such as “obviously” or “of course” can be used.

ex. “Why would this candidate make a good president? Because obviously they are the best person for the job.”

Post hoc, ergo propter hoc

Latin for “After this, therefore, because of this” Asserting a causal connection between two events simply because one happened after the other (in time).

ex. “A black cat crossed my path this morning. That is why my boyfriend broke up with me at lunch.”

The Slippery Slope

asserting a whole chain of events without sufficient evidence of a causal connection.

ex. “The student government is asking for a day off on the Monday after Thanksgiving. If we give in to this request, pretty soon we will be giving them so many days off, they will hardly be in school at all!”

Fallacy of Association

attributing to a person the characteristics of the group (or individual) that he or she is present with or connected to.

ex. “Joey’s cousin is a gang member. Joey must be a criminal.”

Straw man

To describe the opposing position in such weak terms, that it is very easy to refute.

ex. “I want to reform healthcare. But my opponent would rather keep the status quo and do nothing. Doing nothing is not an option.” Probably not true, but easy to refute.

Reduction to the absurd

Taking a statement from your opponent and drawing an absurd conclusion. The idea is if an absurd conclusion comes from the premise, the premise itself must be absurd.

ex. “Opponents of abortion think that abortion is killing. That means they want to throw women who have abortions in jail for murder.”

The non sequitur

Latin for “it does not follow” In general it applies to all fallacies, when one statement does not follow logically from another.

ex. King David: “He is a good man. He must be bringing good news.” 2 Samuel 18:27

first rule of definitions

A definition should be composed of a genus and a difference.

ex. A human is an animal (genus) that is rational, that is, able to think and choose (difference).

genus

(kind) tells us something essential about the thing, though incompletely. Should be as close as possible to what we are trying to define.

difference

some aspect of the thing that will set it off definitively from others which share the same genus. Should be essential to the thing, if we can know it. If not, we should choose some other characteristic.

second rule of definitions

The definition and the thing defined (the definitum) should be convertible.

convertible

Your definition is so complete, that when you switch the word and the definition around, it still makes sense. If you turn the definition into a question, the word being defined is the only possible answer.

ex. An animal that possesses reason is a human.

third rule of definitions

The definition should signify more clearly than the thing defined. Avoid unfamiliar or overly technical language, metaphor, ambiguous words, or negation.

fourth rule of definitions

In the definition, do not include the word you are defining, or any form of that word.

ex. Clothing is cloth you wear on your body.

fifth rule of definitions

The definition must be universal, but not too universal. It cannot apply to a particular example.

ex. A girl is my sister Miranda ←not universal ex. A fish is a living thing in water ← too universal

proposition

composite expression that signifies what is true or false. Concepts are combined or divided, such that the combination or division can be true or false.

• Combining (x is y): A dog is an animal.

• Dividing (x is not y): A dog is not a fish.

deductive logic

a logical approach where you progress from general ideas/premises to reach specific conclusions. (isosceles triangle example)

• syllogism example.

Syllogism

an act of reasoning. It is like math with words. Two propositions, each of which are true, are combined so that we arrive at a third proposition, a new truth. Must be valid as it follows logically.

All humans are mortal (major premise) Spellman students are humans (minor premise) All Spellman students are mortal (conclusion)

major premise, minor premise, and conclusion.

three propositions that compose a syllogism.

inductive logic

Complies facts and evidence to arrive at a conclusion. It allows us to arrive at solid conclusions, but not with the certitude of deductive logic. They are used by:

• Judges and juries to determine guilt or innocence

• Scientists to formulate hypotheses.

• Journalists to report news.

• Doctors to diagnose a disease.