Logical Reasoning Lecture 2

# Logical Reasoning Lecture 2 - 1 Logical Reasoning Lecture#2...

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1 Logical Reasoning Lecture #2 I. Concepts A concept is an idea that represents a class of things that are grouped together by language. A referent of a concept is the particular things that are picked out by the concept. The concept DOG picks out particular dogs (Lassie, Benji, Spot, my dog, your dog, etc.). II. Propositions (A) What are Propositions? Propositions are the units of thought and speech. Propositions can be asserted through statements A proposition involves a concept (which identifies a class of things) and asserts something about the members of that class. (B) Propositions and Sentences * A proposition is either true or false. Propositions are normally expressed through sentences.

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2 Not all sentences express propositions. For example: - Interrogative sentences ask questions: “Did you do your work today?” - Imperative sentences give commands: “Do your work.” - Emotive sentences express emotions: “Ouch!” Propositions are usually expressed through declarative sentences. * Declarative sentences assert that something is a fact. Examples: Bill Clinton was President. Washington is a city. The next president will be a Republican. Declarative sentences all involve a subject (Bill Clinton, Washington, The next president) and predicate (was President, is a city, will be a Republican). Declarative sentences are the linguistic vehicle that we use to express a proposition. Propositions must be distinguished from sentences, however, because: (i) Two different sentences can express the same proposition. (ii) A single sentence may express more than one
proposition (C) Propositions and Word Meaning Two different sentences can express the same proposition when the sentences uses two different words for the same thing or for the same concept. Examples: The forty-second president was impeached. Bill Clinton was impeached. I have a red car. I have a red automobile. The enemy intelligence officer was terminated with extreme prejudice. The enemy spy was killed. What about? - Montana was a good quarterback. - Montana was a good football player. The concepts of QUARTERBACK and FOOTBALL PLAYER are not the same concept. So, these two sentences do not express the same proposition. What about?

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## This note was uploaded on 04/15/2008 for the course PHIL 111 taught by Professor Steinbeck during the Spring '08 term at Bridgewater State University.

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Logical Reasoning Lecture 2 - 1 Logical Reasoning Lecture#2...

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