Logical Reasoning - Logical Deduction - Discussion

In each question below are given two statements followed by two conclusions numbered I and II. You have to take the given two statements to be true even if they seem to be at variance from commonly known facts. Read the conclusion and then decide which of the given conclusions logically follows from the two given statements, disregarding commonly known facts.

Give answer:

  • (A) If only conclusion I follows
  • (B) If only conclusion II follows
  • (C) If either I or II follows
  • (D) If neither I nor II follows and
  • (E) If both I and II follow.

15. 

Statements: All fishes are grey in colour. Some fishes are heavy.

Conclusions:

  1. All heavy fishes are grey in colour.
  2. All light fishes are not grey in colour.

[A]. Only conclusion I follows
[B]. Only conclusion II follows
[C]. Either I or II follows
[D]. Neither I nor II follows
[E]. Both I and II follow

Answer: Option A

Explanation:

Since one premise is particular, the conclusion must be particular and should not contain the middle term. So, it follows that 'Some heavy things are grey in colour'. I is a cumulative result of this conclusion and the first premise. Thus, only I holds.

Rajeev Kumar said: (Dec 23, 2010)  
2nd conclusion is full inversion of 1st conclusion. So it should be valid.hence answer should be E.

Rocky said: (Sep 14, 2011)  
According to the rule of syllogism, the middle term should not be there in the conclusion. Here fishes is the middle term. So the conclusion should not contain the middle term.

Bhushan said: (Sep 8, 2012)  
If a term is not distributed in premise, it should not be distributed in conclusion. Heavy is not distributed according to second premise,so it shouldn't be distributed in conclusion.In 1st conclusion heavy is distributed.So it is not valid.Hence answer is D.

Abhishek Rao said: (Sep 3, 2013)  
Some fishes are heavy does not mean all heavy fishes are grey.

Abhiman Sahoo said: (Sep 6, 2013)  
If one of the premises is particular (contains some) then conclusion must be particular.

Hence answer is D.

Abhi said: (Sep 29, 2013)  
Answer is D.

In this case conclusion must start with some.

The conclusion will be some heavy things are gray in color.

Ila said: (Aug 15, 2014)  
Conclusion should be D as the premises is particular so the conclusion should also be particular.

V.Pandieswari said: (Sep 25, 2014)  
Answer is D, statement 1 is universal positive and statement 2 is particular positive so conclusion must in the form of particular.

Saurabh Choudhary said: (Sep 30, 2014)  
As color is non distributive and heavy fishes are non distributive. And statement B is particular therefore conclusion will be.

Some heavy fishes are grey in color.

So D will be the answer.

Piyush Baghla said: (Oct 24, 2014)  
A --- is correct.

Just make a Venn diagram to understand this.

Kanwar said: (Nov 19, 2014)  
The question has error as assumption 1 written in question doesn't match as that explained in explanation see carefully.

Ako Venuh said: (Mar 26, 2015)  
The conclusion cannot contain the middle term (fishes). And since one of the premises is particular the conclusion should be particular.

Trishul said: (Jul 17, 2015)  
@Ako Venuh,

Fishes is the middle term but heavy fishes is not the middle term. Heavy fishes is a completely distributed subset of both fishes and heavy.

Rajesh Jha said: (Jul 23, 2015)  
Answer should be D. Because to have a Universal positive conclusion we need to have both the sentences to be universal positive.

And the Rule of Either 1 or 2 also can not be applied as the subject and predicates are not same. Hence only D.

Sreeguru said: (Sep 3, 2015)  
Strongly would say its D.

Pooja said: (Sep 4, 2015)  
According to syllogism Answer must be D. Correct Answer should be "Some heavy fishes are grey in color".

Mona said: (Nov 4, 2015)  
According to Venn diagram A is correct.

Anshu Ranjan said: (Jan 24, 2016)  
Middle word should not be there in conclusion. So answer is D and also one particular premise gives the particular conclusion and even if we converse the conclusion or by conversion of any other premises we don't able to get the required conclusion. So answer should be some heavy things are grey in color.

Sourav Bibhor said: (Mar 7, 2016)  
Middle term should not come in the solution so it is invalid, answer should be particular affirmative should.

Raju said: (Jun 29, 2016)  
Even I think the answer is D. Can someone tell it in venn diagram method?

Dushyant Ingle said: (Jun 30, 2016)  
I think both are correct because light fish are not grey.

Arpan Banerjee said: (Jul 10, 2016)  
Yes, The answer should be option D.

Rajeev Sati said: (Sep 8, 2016)  
There conclusion must be particular and 1st conclusion is not particular. So the answer should be D.

Riddle42 said: (Oct 15, 2016)  
The right answer is A.

We know the statements: Some fishes are heavy. ALL (including all of them that are heavy) fishes are GREY in colour. So that makes conclusion number one right.

1. All heavy fishes are grey in colour.

Anisha said: (Dec 6, 2016)  
All those people who claim that A is the correct answer are wrong. The reason is because of this:
The answer SHOULD start from "Some" and SHOULD NOT have the middle term (fishes) at all.

The answer would be: Some heavy things are grey. Some grey things are heavy. [These 2 sentences are converse of each other.]

Why? Because check "Case 5'' in this link: http://www.indiabix.com/logical-reasoning/logical-deduction/formulas
That diagram's Venn diagram is how the Venn diagram should be.

Yes, a statement I is "grammatically and logically" correct. But that's not the conclusion because it is simply rephrased. We are here to find the logical deduction, not to rephrase the question based on a Venn diagram. If that's what we have to do, then all other answers should also follow "rephrasing" instead of "deducing". Hence, the explanation is vague.

D is the correct answer. I am 300% sure.

Abhi said: (Dec 19, 2016)  
According to me, D is the answer.

Dr. Mangai said: (Mar 15, 2017)  
I too think D is the right option with the Ven Diagram method.

Vijay said: (Sep 9, 2017)  
NO, the answer is A is correct according to Ven Diagram.

Dipesh said: (Sep 13, 2017)  
The answer is D please correct the answer.

Tanveer said: (Sep 23, 2017)  
The correct answer is A. No, matter what a fish is (heavy or not), it's grey in colour.

Somesh More said: (Dec 15, 2017)  
The answer to this question is d.

As conclusion 2 fails because there is nothing mentioned about light fishes.

And one fails because it is not mandatory that all heavy should be grey, if it was "some heavy are grey" then conclusion one would follow.

Bill said: (Aug 28, 2018)  
It has to be A.

If all fish are grey then how can a thing that isn't grey be a fish as they are all grey.

Bonny Salout said: (Sep 6, 2018)  
Can someone please explain this with a Venn diagram?

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