Logic, Theories of Human Nature

Argument definition?

Chain of reasoning or train of thought

Premises definition?

Unargued starting points

Conclusion definition

The Point supported by the premises

Inference definition

The connection by which the conclusion follows from the premises

Deductive argument definition?

Argument where the conclusion is deduced from the given premises

Deductive argument example?

1. Socrates is a human being

2. All human beings are mortal

therefore,

3. Socrates is mortal

Valid argument definition

An argument that if all its premises are true then its conclusion must be true.

Is it possible in a valid argument to have all its premises be true but its conclusion false?

No

What makes an argument invalid?

An argument where the conclusion could still be false even if all the premises are true

What does the word valid mean in this class

The point you make is relevant or appropriate

How can you tell if a deductive argument is valid or not?

By looking at its form.

In a deductive argument that uses “All“ or “Some“ which notations does it use?

Subject(S), Predicate(P), and Middle term(M)

What is an example of a valid argument

1. Socrates is a human being

2. All human beings are mortal

therefore,

3. Socrates is mortal

S=socrates, P=mortal, M=human being

1. S is M

2. All M are P.

Therefore

3. S is P

When using S, M, and P which form is always invalid?

1. S is M

2. All P are M

Therefore

3. S is P

Are false premises and true conclusions possible?

Yes

Example of a deductive argument form?

1. All triangles are 4-sided figures

2. All 4-sided figures are 3-sided figures

therefore

3. All Triangles are 3-sided figures

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1. All S(triangle) are M(4 sided)

2. All M(4-sided) are P(3 sided)

therefore

3. All S(triangle) are P(3-sided)

What is a sound argument?

An argument that is valid and all its premises are true.

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This argument is valid but unsound

1. All triangles are 4-sided figures

2. All 4-sided figures are 3-sided figures

therefore

3. All Triangles are 3-sided figures

What does modus mean?

Mode or method

What does ponens mean?

affirming

What does tollens mean

Denying

What does Modus ponens mean?

A mode of affirming

What does Modus Tollens Mean?

A mode of denying

Example of Modus Tollens(Valid)

1. If it is a dog then it is an animal

2. It is not an animal

Therefore

3. It is not a dog

(it is the case that every dog is an animal, then by denying that a thing in question is an animal, then you must also be denying that it is a dog.)

Example of Affirming the consequent(Invalid)

1. If it si a dog then it is an animal

2. It is an animal

Therefore

3. it is a dog

(Even if the two premises are true, by affirming that a given thing is an animal does not follow that it is a dog because it can be any other animal, such as a cat)

Example of denying the antecedent(invalid)

1. If it is a dog, then it is an animal

2. It is not a dog

therefore

it is not an animal

(Even if the two premises are true, by denying that a given thing is a dog does not follow that it is not an animal since the thing can be another kind of animal, such as a cat)

Example of Disjunctive Syllogism(valid)

1. Either a natural number is even or it is odd

2. This natural number is not even

Therefore

3. it is odd

(If the two premises are true, that is if there are only two options and you deny that it is one of them, you must be affirming the other option.)

What is an inductive argument?

An argument in which the conclusion is supported by evidence from experience. The conclusion is only probable, not guaranteed.

General form of an inductive argument?

1. A1 is a B.

2. A2 is a B.

3. A3 is a B.

4. A4 is a B.

Therefore

5. Probably the next A will also be a B.

What is a fallacy?

A mistake in reasoning

What is an Ad Hominem Argument?

Attacking the character of the person instead of the argument.

What is an argument from authority

Appealing to an authority as justification for one’s belief.

What is arguing in a circle/begging the question

Using the conclusion as its premise to prove the conclusion

Ex: I believe in God because the Bible says so, and I believe in the Bible because it is the word of God.

What is an argument from ignorance?

Appealing to the opponent’s ignorance as the justification for one’s belief

Ex: I believe in Superman since you cannot disprove its existence

What is a false dilemma?

When only two alternatives are given but there are several other possibilities/options.

What is a straw man argument

Misrepresents or distorts an opponent’s argument and thereby attacks an inferior version.

What is the principle of charity?

Giving the opponent all the benefits of doubt and constructs the strongest version of the argument presented

What is the fallacy of composition

When one infers from the parts to the whole.

Ex: Since every page is very light, the whole book must be light.

What is the fallacy of division?

When one infers from the whole to its parts.

Ex: Since this is a very heavy book, then the pages must also be very heavy.