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A valid argument is often defined as one in which it is not [#permalink]
28 Jun 2008, 23:38

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A

B

C

D

E

Difficulty:

95% (hard)

Question Stats:

33% (02:15) correct
67% (01:23) wrong based on 734 sessions

A valid argument is often defined as one in which it is not possible for all the premises to be true and the conclusion false. A circular argument is sometimes defined as one in which one of the premises is identical to the conclusion.

From these definitions we can infer that...

(A) Every circular argument is valid as long as its premises are true. (B) Every valid argument is circular. (C) No circular argument is valid. (D) Some circular arguments are valid, and some are not. (E) Some circular arguments are not valid, and some valid arguments are not circular.

Re: CR Circular Argument [#permalink]
29 Jun 2008, 00:17

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IMO D.

Few Premises are valid and few are not within Valid arguments(VA). But conclusion is valid(not false). in circular argument(CA) one of the premise is identical with conclusion. Therefore, CA with one valid premise(identical) is a valid VA and some CA without identical premise is invalid VA. Hence D. _________________

If You're Not Living On The Edge, You're Taking Up Too Much Space

Re: CR Circular Argument [#permalink]
29 Jun 2008, 05:01

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Expert's post

durgesh79 wrote:

A circular argument is sometimes defined as one in which one of the premises is identical to the conclusion.

So, in a circular argument, if the premises are all true, the conclusion must be true: the conclusion is the same as one of the premises.

durgesh79 wrote:

A valid argument is often defined as one in which it is not possible for all the premises to be true and the conclusion false.

Since the conclusion of a circular argument is the same as one of the premises, if the premises are all true, the conclusion cannot be false. Thus, circular arguments are 'valid arguments', according to the definitions. A. _________________

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Re: CR Circular Argument [#permalink]
29 Jun 2008, 05:27

IanStewart wrote:

durgesh79 wrote:

A circular argument is sometimes defined as one in which one of the premises is identical to the conclusion.

So, in a circular argument, if the premises are all true, the conclusion must be true: the conclusion is the same as one of the premises.

durgesh79 wrote:

A valid argument is often defined as one in which it is not possible for all the premises to be true and the conclusion false.

Since the conclusion of a circular argument is the same as one of the premises, if the premises are all true, the conclusion cannot be false. Thus, circular arguments are 'valid arguments', according to the definitions. A.

Re: CR Circular Argument [#permalink]
29 Jun 2008, 05:52

A circular argument is sometimes defined as one in which one of the premises is identical to the conclusion.

So, in a circular argument, if the premises are all true, the conclusion must be true: the conclusion is the same as one of the premises.

durgesh79 wrote: A valid argument is often defined as one in which it is not possible for all the premises to be true and the conclusion false.

Since the conclusion of a circular argument is the same as one of the premises, if the premises are all true, the conclusion cannot be false. Thus, circular arguments are 'valid arguments', according to the definitions. A.

durgesh79 wrote:

A circular argument is sometimes defined as one in which one of the premises is identical to the conclusion.

So, in a circular argument, if the premises are all true, the conclusion must be true: the conclusion is the same as one of the premises.

durgesh79 wrote:

A valid argument is often defined as one in which it is not possible for all the premises to be true and the conclusion false.

Since the conclusion of a circular argument is the same as one of the premises, if the premises are all true, the conclusion cannot be false. Thus, circular arguments are 'valid arguments', according to the definitions. A.

Hi,

Shouldn't the above explanation also make option D right. ? D. Some circular arguments are valid, and some are not.

Re: CR Circular Argument [#permalink]
29 Jun 2008, 06:04

MamtaKrishnia wrote:

A circular argument is sometimes defined as one in which one of the premises is identical to the conclusion.

So, in a circular argument, if the premises are all true, the conclusion must be true: the conclusion is the same as one of the premises.

durgesh79 wrote: A valid argument is often defined as one in which it is not possible for all the premises to be true and the conclusion false.

Since the conclusion of a circular argument is the same as one of the premises, if the premises are all true, the conclusion cannot be false. Thus, circular arguments are 'valid arguments', according to the definitions. A.

durgesh79 wrote:

A circular argument is sometimes defined as one in which one of the premises is identical to the conclusion.

So, in a circular argument, if the premises are all true, the conclusion must be true: the conclusion is the same as one of the premises.

durgesh79 wrote:

A valid argument is often defined as one in which it is not possible for all the premises to be true and the conclusion false.

Since the conclusion of a circular argument is the same as one of the premises, if the premises are all true, the conclusion cannot be false. Thus, circular arguments are 'valid arguments', according to the definitions. A.

Hi,

Shouldn't the above explanation also make option D right. ? D. Some circular arguments are valid, and some are not.

I think D is wrong due to the expression of "some (CA) are not (valid)". CA is premise = conclusioin. It should be valid since, under CA, if premise is true, conclusion is to be true, if p is not true, then conclusion is not true. Any other thoughts?

Re: CR Circular Argument [#permalink]
29 Jun 2008, 12:39

Expert's post

Ashwin_Mohan wrote:

I would say D,

Reason:

Premise 1: True

Premise 2 True

Conclusion : True (as conclusion = Premise 1)

Thus Valid Argument

Premise 1: True

Premise 2 : False

Conclusion : True (as conclusion = Premise 1)

Not a valid argument in this case.

hence sometimes valid and sometimes invalid.

From the question, "A valid argument is often defined as one in which it is not possible for all the premises to be true and the conclusion false." There is nothing in this definition to suggest that false premises make an argument invalid. _________________

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Last edited by IanStewart on 29 Jun 2008, 13:42, edited 1 time in total.

Re: CR Circular Argument [#permalink]
29 Jun 2008, 13:39

1

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Expert's post

Ashwin_Mohan wrote:

There are only 2 values that the premise and conclusions can take. True and False. Thus the question states that

A valid argument is often defined as one in which it is not possible for all the premises to be true and the conclusion false

from this we can infer that if one of the premises is not true(= false) then the conclusion cannot be true (for a valid argument that is!!)

That is not a valid inference. While the question doesn't say that there are only two values the premise and conclusion can take, it doesn't make a difference if we assume this to be the case. An argument is valid if:

If the premises are true, the conclusion is true.

The lone inference we can make from this is the contrapositive (from "If A then B" you can always conclude "If not B then not A"). That is, we can conclude:

If the conclusion is false, the premises are false (well, at least one of them is).

The inference you have made, "If the premises are false, the conclusion is false", is called the 'inverse'. That is, you've translated "If A then B" into "If not A then not B". This is not a legitimate inference to draw, as I will illustrate with an example. Suppose I'm standing next to a swimming pool, and have no shelter nearby. Then the following may be true:

"If it rains, I get wet."

We can certainly deduce the contrapositive:

"If I'm not wet, it's not raining."

We cannot conclude the inverse:

"If it's not raining, I'm not wet". I might be in the swimming pool.

Equivalently, we cannot deduce the converse (I say equivalently, because the converse is the contrapositive of the inverse- they're logically the same):

"If I'm wet, it's raining." Again, I might be swimming. _________________

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If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com

Re: CR Circular Argument [#permalink]
29 Jun 2008, 15:46

Nice explanation..here's some additional info....

Here's how a circular argument would look like

Premise 1 : The woman says she is not mad Premise 2 : Whatever the woman says is true Conclusion : The woman is not mad. (= premise 1)

more like A-->B-->C-->A

Anyone who rejects the argument’s conclusion should also reject at least one of its premises (the one that is the same as its conclusion), and so should reject the argument as a whole.

Anyone who accepts all of the argument’s premises already accepts the argument’s conclusion, so can’t be said to have been persuaded by the argument. In neither case, then, will the argument be successful.

Re: CR Circular Argument [#permalink]
29 Jun 2008, 21:12

Good discussion Guys, the OA is A. Below is the OE, which i dint understand.

"(A) Some people find this paradoxical, but it follows directly that circular arguments are valid. If the premises are true, and the conclusion is one if the premises, it must be true. Another trick here is the word 'valid'. Just because an argument is valid, does not mean it is true. Many people will make that false assumption and be thrown off on this question."

took long time to understand this. But agree with A.

Valid argument --> Often, all premises cannot be true, conclusion cannot be false Circular argument --> sometimes, premise = conclusion

(A) Every circular argument is valid as long as its premises are true.

If premises are true --> conclusion is true (Circular argument) --> and conclusion cannot be false in valid argument --> In this case, conclusion is true and hence circular argument is valid as long as its premises are true.

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