Introduction to Logic Lecture 1 What is Critical Reasoning? By David Kelsey

Course Objectives Thinking Rationally: We will learn how to think correctly or rationally or logically. For someone to think rationally just means that she, from her set of beliefs, makes inferences that are justified given the laws of logic.

The Laws of Logic The laws of logic: dictate just which inferences we can make. They are rules for making good inferences. 2 examples: Modus Ponens: Modus Tollens: Sentence letters

Inferences An inference: a statement that follows from one or more other statements.

Statements A statement is a proposition. A proposition is the meaning of a sentence: Just like words have meanings, sentences have meanings.

Propositions The form of a proposition: ‘it is the case that…’. Propositions are true or false.

Propositions & Sentences A sentence does two different things: it both expresses a proposition and asserts a proposition. The expressed proposition: the literal meaning of the words of that sentence.

Expressing a proposition For a sentence to express a proposition: is for that sentence to toss the proposition up in the air, so to speak. It is to put the proposition up for usage. Knowing what proposition a sentence expresses:

The asserted Proposition Making use of a proposition: Just how a sentence makes use of the proposition a sentence expresses determines it’s actual or intended meaning. The proposition asserted: the actual or intended meaning of a sentence The actual or intended meaning of a sentence: What the speaker or writer of the sentence means when she writes or says it.

Miscommunication Miscommunication: When the hearer doesn’t take the sentence to assert what the speaker intends

Sarcasm Other kinds of sentences: Sarcasm: The messy roomate: “She always takes out the trash”. This sentence expresses: But the sentence asserts: Other occassions when meaning splits:

Arguments Arguments: when one proposition is inferred from one or more other propositions Other definitions of an Argument

Arguments Argument: a position supported by reasons for its truth. To take a position: An issue: what is raised when one considers whether or not a proposition is true.

Issues Issues: we might go as far as to say that an issue just is a question. Intelligent life: Safety belt law: Mac vs. Pc:

Arguments & Positions Arguments & Positions: so when we take a position on an issue and support it with reasons we have given an argument. Intelligent life: Safety Belt law: Mac vs. Pc:

Conclusions & Premises Arguments: The conclusion of an argument: The premises of an argument: Examples: Socrates again April showers

What an argument isn’t What an argument isn’t: Let us be a bit clearer about what an argument is by stating what it isn’t. Not a Fight: Not Persuasion:

Persuasion Persuasion vs. Argument: An argument offers support for some claim, its conclusion. Persuasion needn’t offer any support for a point. Not Logic: It merely attempts to get you to believe a point. Persuasion through rhetoric: Rhetoric: is “a broad category of linguistic techniques people use when their primary objective is to influence beliefs and attitudes and behavior”

Arguments vs. Explanations Explanation of X: If one gives an explanation about some thing X, one gives some details about X with the hope of coming to better understand X. Example: fixing a flat tire

Recognizing Arguments Conclusion Indicators: find the conclusion of an argument by looking for conclusion indicators. Examples of Conclusion Indicators: therefore, hence, and others Premise Indicators: find the premises of an argument by looking for premise indicators Examples of Premise Indicators: because, since, and others

An introduction to formalizing an argument Challenging an argument: In challenging an argument you must first formalize it. Formalizing an argument: Is the reconstruction of that argument in its most simplified form.

Explicit Premises Explicit premises: asserted by the words of the text.

Implicit Premises Implicit or unstated premises: entailed by the words of the text. Bloodhound example:

Factual claims Arguments and Claims: Factual Claims Either true or false. Established methods Generally Established Criteria Settling Disagreement Example: Water is H2O

Non-factual claims Non-factual claims: No established methods Can’t settle Disagreement Some examples:

Value Claims Value claims: non-factual claims that assert that some moral property is instantiated in some object or action or event. Properties and Moral Properties Never Ought from Is…