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# need help on this syllogism question please!

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Manager
Joined: 04 Jan 2013
Posts: 80

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13 Jan 2013, 12:57
Statements :
1. All women are mothers.
2. All mothers are sisters.
Conclusions :
1. All women are sisters.
2. Some women are not
sisters.
Since both the premises
are affirmative, the
conclusion must be
affirmative. So, conclusion
2 cannot follow.

hi guys this is a syllogism question i copied from indiabix..i just wanted to know why conclusion 2 does not follow..if we take conclusion 1 as a convertend then conclusion 1 would gives us the following converse;some women are mothers..now,my question lies on the fact that if some women are mothers then the arguement that some women are not mothers would also be true according to the contrary rule(which states that if one of the two contraries is true then the other is also true)on the tradition square of opposition..i need your replies please

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Joined: 23 Mar 2011
Posts: 1113
Concentration: Healthcare, Strategy
Schools: Duke '16 (M)

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13 Jan 2013, 16:44
chiccufrazer1 wrote:
Statements :
1. All women are mothers.
2. All mothers are sisters.
Conclusions :
1. All women are sisters.
2. Some women are not
sisters.
Since both the premises
are affirmative, the
conclusion must be
affirmative. So, conclusion
2 cannot follow.

hi guys this is a syllogism question i copied from indiabix..i just wanted to know why conclusion 2 does not follow..if we take conclusion 1 as a convertend then conclusion 1 would gives us the following converse;some women are mothers..now,my question lies on the fact that if some women are mothers then the arguement that some women are not mothers would also be true according to the contrary rule(which states that if one of the two contraries is true then the other is also true)on the tradition square of opposition..i need your replies please

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1.) I wasn't able to grasp after the red part. So will explain the question in red.
2.) this is not a gmat question. It will be better for you if you study from a better source.
3.) answer to the red part:
if there are 5 women, who are all mothers. And these 5 mothers are all sisters, then "Some women are not sisters" does not hold true.
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Joined: 02 Jul 2012
Posts: 1223
Location: India
Concentration: Strategy
GMAT 1: 740 Q49 V42
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13 Jan 2013, 22:27
A better framing of conclusion two would be "Some women may not be sisters"
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14 Jan 2013, 00:24
chiccufrazer1 wrote:
Statements :
1. All women are mothers.
2. All mothers are sisters.
Conclusions :
1. All women are sisters.
2. Some women are not
sisters.
Since both the premises
are affirmative, the
conclusion must be
affirmative. So, conclusion
2 cannot follow.

hi guys this is a syllogism question i copied from indiabix..i just wanted to know why conclusion 2 does not follow..if we take conclusion 1 as a convertend then conclusion 1 would gives us the following converse;some women are mothers..now,my question lies on the fact that if some women are mothers then the arguement that some women are not mothers would also be true according to the contrary rule(which states that if one of the two contraries is true then the other is also true)on the tradition square of opposition..i need your replies please

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I don't know which book you are following to get your concepts straight but it is certainly not working out. I am not sure where the fault lies.

'All women are mothers' implies 'some women are mothers' - Correct
'Some women are mothers' implies 'some women are not mothers' - Incorrect

'Some' is a case of partial information. You only know about some women. You don't know about the others. In a class, say, there are 10 students. I ask only 3 of them - 'Are you from Michigan?' All three say 'Yes'. I can now say that 'some of you are from Michigan'. The point is - I don't know about the rest.. It is possible that they are from Michigan too. It is possible that some of them are not from Michigan. I don't know. Hence, 'some people are' does not imply 'some are not'.
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Re: need help on this syllogism question please!   [#permalink] 14 Jan 2013, 00:24
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