Chapter 1: What is Logic? Flashcards

(17 cards)

1
Q

What is a logical argument?

A

A set of sentences structured with premises intended to offer support for a conclusion. Anatomy: first sentences are premises, last sentence is the conclusion. An argument whose premises have no relation with the conclusion can still be defined as such.

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2
Q

What are premises? Give some premise indicators.

A

Starting points, used to lend support to the conclusion.

Indicators: since, because, given that

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3
Q

What is a conclusion? Give some conclusion indicators.

A

The claim the argument is trying to establish.

Indicators: therefore, hence, thus, then, so

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4
Q

What are propositions?

A

Sentences that can be true or false (not questions; regardless of facts or opinions).

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5
Q

What do we consider as a sentence?

A

A sentence that expresses a proposition and can either be true or false. Answers (e.g. “I do not know how to write.”) Imperatives (e.g. “Wake up!” “Leave!”) Not questions, not exclamations.

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6
Q

Two ways an argument could be weak?

A
  1. At least one of its premises might be false.

2. Premises might fail to support the conclusion or fail to support it sufficiently strong.

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7
Q

What does it mean for an argument to be deductively valid?

A

Argument is deductively valid iff it is impossible for all the premises to be true while the conclusion is false.

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8
Q

Define a sound argument.

A

An argument is sound iff it is valid and all of its premises are true.

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9
Q

What does it mean for a sentence to be impossible?

A

There is no possible way for it to be true. Must be false. (E.g. Pigs can fly and pigs cannot fly) [just “pigs can fly” is NOT impossible!]

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10
Q

Define contingent sentences

A

Sentences that could be true, or could be false. (E.g. It is raining) A contingent sentence is a sentence that is neither a tautology nor a contradiction.

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11
Q

Define logical truth/ tautology

A

Sentences that must be true no matter what (e.g. It is either cold today, or it is not cold today)

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12
Q

Define contradiction and what it means for a sentence to be logically false.

A

Logically false = contradiction. Sentence is always false no matter what. (E.g. “There is an earthquake happening here right now and there are never earthquakes here.”)

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13
Q

When do we say two sentences are logically equivalent?

A

When they necessarily (always) have the same truth value (i.e. Sentence X <=> Sentence Y)

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14
Q

What does it mean for a set of sentences to be inconsistent?

A

When the sentences could not all be true at the same time.

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15
Q

What does it mean for a set of sentences to be consistent?

A

When the sentences could all be true at the same time.

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16
Q

What does a logical language being bivalent mean?

A

Bivalent = two-valued = true and false are the only possible truth values for the language

17
Q

Classical logic?

A

The logic system we are using. Every sentence is either true or false (exactly 1 truth value)