GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 18 Dec 2018, 13:36

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

## Events & Promotions

###### Events & Promotions in December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
• ### Happy Christmas 20% Sale! Math Revolution All-In-One Products!

December 20, 2018

December 20, 2018

10:00 PM PST

11:00 PM PST

This is the most inexpensive and attractive price in the market. Get the course now!
• ### Key Strategies to Master GMAT SC

December 22, 2018

December 22, 2018

07:00 AM PST

09:00 AM PST

Attend this webinar to learn how to leverage Meaning and Logic to solve the most challenging Sentence Correction Questions.

# A valid argument is often defined as one in which it is not

Author Message
TAGS:

### Hide Tags

Director
Joined: 27 May 2008
Posts: 525
A valid argument is often defined as one in which it is not  [#permalink]

### Show Tags

28 Jun 2008, 23:38
5
16
00:00

Difficulty:

95% (hard)

Question Stats:

37% (01:46) correct 63% (01:59) wrong based on 1067 sessions

### HideShow timer Statistics

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.
Director
Joined: 25 Oct 2006
Posts: 546

### Show Tags

29 Jun 2008, 00:17
1
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

GMAT Tutor
Joined: 24 Jun 2008
Posts: 1322

### Show Tags

29 Jun 2008, 05:01
2
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.
_________________

GMAT Tutor in Toronto

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

Manager
Joined: 02 May 2008
Posts: 79

### Show Tags

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.
Manager
Joined: 22 Jun 2008
Posts: 83

### Show Tags

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?
Manager
Joined: 25 Nov 2006
Posts: 219

### Show Tags

29 Jun 2008, 12:19
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.
GMAT Tutor
Joined: 24 Jun 2008
Posts: 1322

### Show Tags

Updated on: 29 Jun 2008, 13:42
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.
_________________

GMAT Tutor in Toronto

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

Originally posted by IanStewart on 29 Jun 2008, 12:39.
Last edited by IanStewart on 29 Jun 2008, 13:42, edited 1 time in total.
Manager
Joined: 25 Nov 2006
Posts: 219

### Show Tags

29 Jun 2008, 12:57
3
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!!)
GMAT Tutor
Joined: 24 Jun 2008
Posts: 1322

### Show Tags

29 Jun 2008, 13:39
1
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.
_________________

GMAT Tutor in Toronto

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

Manager
Joined: 25 Nov 2006
Posts: 219

### Show Tags

29 Jun 2008, 15:46

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.
Director
Joined: 27 May 2008
Posts: 525

### Show Tags

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."
VP
Joined: 17 Feb 2010
Posts: 1106

### Show Tags

24 Jul 2010, 14:47
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.
Manager
Joined: 06 Jul 2010
Posts: 76

### Show Tags

26 Jul 2010, 07:26
+1 for A. But a good challenging CR Thanks durgesh79
Senior Manager
Joined: 18 Sep 2009
Posts: 283

### Show Tags

25 Jul 2011, 06:10
Thank you seekmba for your explanation.
Manager
Joined: 29 Sep 2008
Posts: 94

### Show Tags

26 Jul 2011, 00:57
certainly A is true...for a valid argument conclusion should be true while some premise can be true.Therefore for circular argument to be true the premise should be true as the truth for the conclusion is mandatory
Intern
Joined: 25 Jul 2011
Posts: 28
Location: United Kingdom
Concentration: Finance, Strategy
Schools: Schulich (A)
GMAT 1: 660 Q49 V31
GPA: 3.13

### Show Tags

27 Jul 2011, 02:28
I think VA Conclusion can be true only when all the premises are true. In a CA if all the premises are true then the conclusion is true and it is equal to VA. Hence A is correct.
Manager
Joined: 06 Jul 2011
Posts: 119
Schools: Columbia

### Show Tags

28 Jul 2011, 02:42
Is it just me or is the language a little iffy.

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.

Look at the part in bold. I know logically it would mean that it is not possible for the conclusion to be false, but I thought it was a trick question and it mean that not all premises to be true AND conclusion must be false. Just thought the language was very awkward.

If that's the case, then u would read it as premise = false / conclusion = false for valid argument. The multiple choices confirmed that my interpretation is wrong, but wasted valuable time in figuring that out.
Manager
Joined: 06 Jul 2011
Posts: 119
Schools: Columbia

### Show Tags

30 Jul 2011, 14:08
Can someone help me with this, I've been thinking about this for 15minutes and still can't figure it out. I can understand why A is correct. But why is D wrong?

Won't by definition if X the Circular = Valid then if !X then Circular != Valid.
Manager
Joined: 21 Nov 2010
Posts: 87
Re: A valid argument is often defined as one in which it is not  [#permalink]

### Show Tags

19 Dec 2011, 16:40
A. All circular arguments are valid since premise is true and conclusion is true (definition of valid from the question).

---------------------------
Give Kudos if you like my post!
Manager
Joined: 13 Aug 2010
Posts: 158
Re: A valid argument is often defined as one in which it is not  [#permalink]

### Show Tags

20 Dec 2011, 03:14
A valid argument= it is not possible for all the premises to be true and the conclusion false.
-- if all premise true then conclusion true
-- if one among the many conclusion false then conclusion can be false
-- if all false then conclusion false

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

so,

(A) Every circular argument is valid as long as its premises are true. Correct,
for a circular arg. premise = conclusion, and this is possible when all the argument in Valid arg. are true. Hope this helps.
Re: A valid argument is often defined as one in which it is not &nbs [#permalink] 20 Dec 2011, 03:14

Go to page    1   2    Next  [ 28 posts ]

Display posts from previous: Sort by