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Informal logic

The basics that make up an argument

Logic

Logic is a formal science that evaluates arguments. Good arguments are those in which premises really do support the conclusion. The argument can be valid or invalid. Logic doesn’t assign truth values. Correct thought.

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It does not mean a verbal fight.

Premises    ConclusionPremises \implies Conclusion.

  • An inference is the reasoning process expressed by an argument.

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Some people sum up their work and they called “the conclusion”; it's a mistake. A conclusion follows from the premises but it doesn't summarize them.

Worked examples

I. List the premises and conclusion of each argument.

II. In most instances, the main conclusion must be rephrased to
capture the author's full intent. Write out what you interpret the main conclusion to be.

Identify an argument

  1. If no evidence is given to prove that such statements are true, then there is no argument.
  1. If they don't support or imply anything, there is no argument. If this passage contains an argument, then these are the premises and that is the conclusion.
  1. If a passage develops a topic but doesn't prove that topic, then there is no argument.
  1. Keep an eye out for premise and conclusion indicator words.
  1. The presence of an inferential relationship between the statements.

Typical kinds of nonarguments

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In real-life situations, authors rarely try to prove something is true when everyone already accepts it.
ArgumentExplanations
Premises. It is to prove that conclusion is the case.Explanans. It shows why the explanandum is the case, so its purpose is to shed light on the explanandum.
Explanandum is an accepted fact.

Conditional propositions and logical equivalence

If pp and qq are propositions, the proposition

if p then qif\text{ p } then \text{ q}

is called a conditional proposition and is denoted p    qp\implies q.

pqp    qp\implies qComments
TTTYou must prove this by assuming the antecedent.
TFFYou don’t prove this since the conclusion is false.
FTTTrue by default or vacuously true, so you don’t prove this.
FFTTrue by default or vacuously true, so you don’t prove this.
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if HYPOTHESIS then CONCLUSION
This is not correct, because it is not an argument.
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if ANTECEDENT then CONSEQUENT
if CAUSE then CONSEQUENCE
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CONSEQUENT if ANTECEDENT
  • Sufficient condition. If A then B. B whenever the occurrence of A is all that is needed for the occurrence of B. A guarantees B, but B might be achieved in other ways.

If X is a cat, then X is an animal.

  • Necessary condition. A cannot occur without the occurrence of B, but B doesn’t guarantee A.

If not B then not A.

If X is not an animal, then X is not a cat.

If X is a cat, then X is an animal.

Si P, entonces Q.
P: X es Y.
Q: Z es W.

Si X es Y, entonces Z es W.

P es una condicion suficiente para que ocurra Q.
Q ocurre porque P.
P no es una condicion necesaria para que ocurra Q.
Q puede ocurrir sin necesidad de que ocurra P.
P garantiza Q, pero Q puede lograrse de otras maneras.
Siempre que ocurra P, pasara Q.
La implicacion no es un argumento, sino su sintesis. Es el fundamento para las inferencias.

Analisis de la tabla de verdad:
True => True True
True => False False Si sabemos que (P=>Q es falso) entonces P es verdaero y Q es Falso.
True =>

Si no Q, no P.
Si no ocurre Q es una condicion suficiente para que no haya pasado P.

no P o Q.

A common mistake is no P ⇒ no Q, it is a mistake because Q can occur if P doesn’t happen.

English equivalences

if states a relation between cause and effect, makes a prediction, or speculates about what might happen. https://www.merriam-webster.com/grammar/if-vs-whether-difference-usage

Worked examples

Restate each proposition in the form of a conditional proposition.

  • Joey will pass the discrete mathematics exam if he studies
    hard.

    p: Joey will pass the discrete mathematics exam

    q: He studies hard.

    q    pq\implies p 

  • Rosa may graduate if she has 160 quarter-hours of credit.

    p: Rosa may graduate.

    q: she has 160 quarter-hours of credit.

    q    pq\implies p

  • A necessary condition for Fernando to buy a computer is that he obtain $2000.

    p: Fernando to buy a computer.

    q: He obtains $2000.

    A necessary condition for pp is qq.

    not q then not p

    p    qp \implies q

  • A sufficient condition for Katrina to take the algorithms course is that she pass discrete mathematics.

    p: Katrina to take the algorithms course.

    q: She passes discrete mathematics.

    A sufficient condition for pp is qq.

    q    pq \implies p

  • Getting that job requires knowing someone who knows the boss.

    p: Getting that job.

    q: Knowing someone who knows the boss.

    A necessary condition for getting a job is knowing someone who knows the boss.

    A necessary condition for p is q.

    p    qp \implies q

  • You can go to the Super Bowl unless you can’t afford the ticket.

    p: You can go to the Super Bowl.

    q: You can afford the ticket.

    p unless not q

    p except on the condition that not q

    A necessary condition for pp is not (not qq).

    A necessary condition for pp is q.

    p    qp\implies q

  • You may inspect the aircraft only if you have the proper security clearance.

    p: You may inspect the aircraft.

    q: You have the proper security clearance.

    A necessary condition for p is q.

    if not q, not p.

    if p, then q.

  • The audience will go to sleep if the chairperson gives the lecture.

    p: The audience will go to sleep.

    q: The chairperson gives the lecture.

    q    pq\implies p

  • The program is readable only if it is well structured.

    p: The program is readable.

    q: It is well structured.

    p    qp\implies q

  • A necessary condition for the switch to not be turned properly is that the light is not on.

    p: The switch is turned properly.

    q: The light is on.

    A necessary condition for not p is that not q.

    if q then p.

    q    pq\implies p

  • Any set of Boolean operators that is sufficient to represent all Boolean expressions is said to be complete. Which of the following is NOT complete? A) {AND,NOT} B) {NOT, OR} C) {AND,OR} D) {NAND} E) {NOR}
  • Provide a method that given a set of Boolean operators, it gives you ifs

Represent the given proposition symbolically

Material Implication: If Pigs Could Fly. (2019, October 04). Retrieved from https://www.dcproof.com/IfPigsCanFly.html

Worked examples

I. Determine which of the following passages are arguments and their conclusion, if it is not, determine the kind of nonargument.

Notes.

Aristotle is the father of logic.

https://www.youtube.com/watch?v=gMpxNrs53yE&ab_channel=MarceloVásconezCarrasco

Deduction, Induction

Evaluate a deductive or inductive argument consists of two steps:

Deductive argument forms

The conclusion follows necessarily from the premises.

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Deductive arguments do not necessarily proceed from general to particular.

Despite the name, mathematical induction is a deductive argument too.

Inductive argument forms

The conclusion follows probably from the premises.

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Inductive arguments do not necessarily proceed from the particular to the general.

Validity, Truth, Soundness, Strength, Cogency

Validity is the relationship between premises and conclusion, do premises support the conclusion?

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An argument is valid because of its form, not because of its content.

Deductive Argument

Deductive arguments are valid, invalid, sound, and unsound.

In a valid deductive argument is impossible to be false given that the premises are true and it’s determined by the argument’s form. So, any deductive argument having true premises and a false conclusion is invalid.

A sound argument is a deductive argument that is valid and has all true premises. Otherwise is called an unsound argument.

Having a superfluous false premise doesn’t change the soundness.

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Successful deductive argument = Sound argument = Valid argument + All true premises
  1. Principio de Identidad
  1. Principio de NO contradicción. ??Principle of explosion??
  1. Principio de Tercero Excluido
  1. Principio de la Razón Suficiente.

https://en.wikipedia.org/wiki/Classical_logic

Inductive Argument

It depends on the uniformity of nature - a mathematical induction depends on natural numbers that are uniform by the Well-Ordering property.

Inductive arguments are strong, weak, cogent or uncogent.

Strong: The conclusion follows the premises.

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Cogent argument = Strong argument + All true premises

Abductive arguments. Retroductive reasoning.

Tipos y ejemplos

TipoEjemplo1Ejemplo2
DeduccionTodos los ratones son roedores.
Speedy González es un ratón.
Speedy González es un roedor.
InduccionSpeedy González es un ratón.
Speedy González es un roedor.
Todos los ratones son roedores.
AbduccionSpeedy González es un roedor.
Todos los ratones son roedores.
Speedy González es un ratón.


Proof methods

Counterexample method

Axiom vs Law

Einstein paper. https://einsteinpapers.press.princeton.edu/vol7-trans/124

Material conditional

Paradoxes of material implication

Language: Meaning and Definition

Varieties of meaning

Language has virtually unlimited functions but, in logic particularly, it conveys information or evokes feelings. The first function, chiefly logic concerned, uses cognitive meaning terms including “legal”, “most often”, “Georgia”, and so; the second one uses emotive meaning terms including “cruel”, “inhuman”, “hapless”, and so forth, statements of this sort very often have both. Since emotive meaning is not mainly concerned with logic, we differentiate the cognitive meaning from the emotive meaning which is a value claim, that is, a claim that something is good, better, or more important than some other thing. We treat these claims as separate statements and as usual, they require evidence to support them. Thus, many writers and speakers use emotive meaning to obscure value claims so the receivers are inclined to swallow them without any evidence.

Cognitive meaning can be defective in two cases affecting the entire statement:

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Fuzzy logic.

Disputes

Verbal disputes are argument conflicts caused by vagueness and ambiguity between individuals. Unless it is clarified, disputes are never resolved. So they arise over the meaning of language.

Factual disputes arise over facts and their interpretation.

The Intension and Extension of terms

In the previous section, you saw that some argument problems arise about vague or ambiguous terms, and even though logic is the evaluation of arguments, those arguments are cleared up by supplying a definition. So, the study of meaning is closely related to logic.

Where is the argument vagueness or ambiguousness?

The basic units of language are words, but your chiefly concern in order to clear up arguments is a term, no general words.

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‘Term’ means the subject of a statement. For example, proper names such as The United States, Senate; common names such as animal, house; descriptive phrases such as books in my library, blue things; and mention of a word such as ‘wherever’ (’wherever’ has eight letters).

Terms are not verbs, adverbs, adjectives, prepositions, conjunctions, and non syntactic arrangements of words.

Even though some words are meaning adjectives and nouns, being a noun, pronoun, proper name, common name, and descriptive phrase is a sufficient condition for being a term.

Cognitive meaning of a term. Logic uses connotation and denotation differently than grammar.
Cognitive meaning example.

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Empty (”null”) class. Terms who have an empty extension.
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Intention determines extension, but conversely, although extension suggests intention, it does not determine intention.

Increasing extension, decreasing intention

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The order of increasing intention is usually that of decreasing extension.

Increasing intention when each term increases attributes than the previous one.

Example:

Programming language, compiled language, oriented-object compiled language, C++.

Increasing extension when each term increases members of the class than the previous one.

Example:

C++, oriented-object compiled language, compiled language, programming language.

How does a term connote a set of attributes?

There are at least two interpretations: an objective approach and a subjective approach. The objective approach holds that a term connotes essential class member attributes. Conversely, our conventional subjective approach holds that a term connotes common attributes in mentally competent people. It's also called conventional connotation. In this approach, connotation and denotation typically remain the same from person to person, but meanwhile, the connotation is stable in time, denotation is not.

Notes

https://www.paultaylor.eu/stable/prot.pdf writes about sense and reference.

https://plato.stanford.edu/entries/definitions/

How do you make a definition?

Purpose of definition

Plato’s view. It expounds on the meaning of their eternal essences.

Most modern logician’s view. It sets out the meaning of a word called definiendum by assignation other words called definiens.

Definition parts.

Some kind of definitions.
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The above definitions are not exhaustive nor mutually exclusive.

Fallacies

What is a fallacy?

Fallacy, sometimes called non sequitur, is a bad argument that appears a good one.

Varieties of fallacies

Informal fallacies

Arguer's goal is to achieve that the reader/listener accepts the conclusion, in fallacies, it's more important than making good arguments. We’re going to enumerate the kind of premises that cause informal fallacies.

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The below fallacies are not exhaustive nor mutually exclusive.

Fallacies of relevance

Fallacies of relevance

Fallacies of weak induction

Worked examples

Identify the fallacies.

Fallacies of presumption, ambiguity, and illicit transference

Fallacies in ordinary language

Notes

A full list is on https://en.wikipedia.org/wiki/List_of_fallacies

https://yourlogicalfallacyis.com/

Analogical Reasoning

Analogical Argument form

Entity A has attributes a, b, c, …, and z.

Entity B has attributes a, b, c, ….

Therefore, entity B probably has attribute z also.

Entity A and entity B are called analogues, where the primary analogue is the first one, and the secondary analogue is the last one.

Procedure.

1) Identify the attributes.

2) Determine if is a causal or systematic relation to the attribute z between a,b, and c, …

Rogers P. Hall (1989). Computational approaches to analogical reasoning: A comparative analysis. , 39(1), 39–120. doi:10.1016/0004-3702(89)90003-9

FitzGerald, M. (2018, October 26). Unit 6: Reasoning by Analogy. Youtube. Retrieved from https://www.youtube.com/watch?v=KerNKoJYd6k&ab_channel=MichaelFitzGerald

Set of principles to evaluate most analogy arguments

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Increasing primary and secondary analogs’ similarity and relevance, stronger the argument.
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Increasing primary and secondary analogues’ similarity numbers, stronger the argument.

Stanford. (2009, September 10). Analogy as the Core of Cognition. Youtube. Retrieved from https://www.youtube.com/watch?v=n8m7lFQ3njk&ab_channel=Stanford

Miller Analogies Test

SAT

https://elearning.shisu.edu.cn/pluginfile.php/36509/mod_resource/content/1/ANALOGIES.pdf

Algorithm

Given an analogy in the form

______ : X :: Y : Z

with options a,b,c,d.

our algorithm must return the missing analogue.

1. find some encode(Y)=Z, such as encode(X)=x, x in options.   
2. find some sequence(Y)=Z, such as encode(X)=x, x in options.   
3. 

We assign greater values conceptual values than encodings. Functions are in our knowledge base.

Notes

https://plato.stanford.edu/entries/definitions/

Reason

“The only definition of rationality that I’ve found that is practically, empirically, and mathematically rigorous is the following: what is rational is that which allows for survival. Unlike modern theories by psychosophasters, it maps to the classical way of thinking. Anything that hinders one’s survival at an individual, collective, tribal, or general level is, to me, irrational.”
Nassim Nicholas Taleb, Skin in the Game: Hidden Asymmetries in Daily Life

What is Truth?

Like beauty, “truth” sometimes depends on the eye of the beholder, and it should not be surprising that what constitutes proof differs among fields. For example,

Eric Lehman, F Thomson Leighton, and Albert R Meyer. Mathematics for Computer Science. revised Wednesday 6th June 2018, 13:43. MIT

Fallacies

https://en.wikipedia.org/wiki/List_of_fallacies

Categories

TODO

Is syllogism an inference rule? (2022, October 01). Retrieved from https://philosophy.stackexchange.com/questions/46653/is-syllogism-an-inference-rule