A theory is either true or false. Galileo's observations of

Question

A theory is either true or false. Galileo’s observations of Jupiter’s satellites showed that the Ptolemaic theory of the motion of celestial bodies is false. Therefore, since the Copernican theory of planetary motion is inconsistent with the Ptolemaic account, Galileo’s observations of Jupiter’s satellites proved the truth of the Copernican theory.

The argument above is open to the objection that it makes the questionable assumption that

(A) Whoever first observed something inconsistent with the truth of the Ptolemaic theory should be credited with having proved that theory false.

(B) There are some possible observations that would be inconsistent with the account given by the Copernican theory but consistent with the account given by the Ptolemaic theory.

(C) The Ptolemaic and Copernican theories, being inconsistent, cannot both be based on exactly the same evidence.

(D) Numerous counterexamples were necessary in order to show the Ptolemaic theory to be false.

(E) The Ptolemaic and Copernican theories, being inconsistent, cannot both be false.

egmat · Accepted Answer

Hi,

Let me share my two cents here.

The question stem requires us to look for the questionable assumption made by the argument.

Let’s first try to deconstruct the argument:
 
 What is the conclusion here?

Galileo’s observations of Jupiter’s satellites proved the truth of the Copernican theory.
 
 What is the basis of this conclusion? 
 
1) A theory is either true or false. Ptolemaic theory is shown to be false.

2) Copernican theory of planetary motion is inconsistent with the Ptolemaic account,
 
Thus, the argument concludes that Copernican theory is true because it is inconsistent with Ptolemaic theory which is false. 
Let’s take an example:

If I say that XYZ flower is red and you say that XYZ flower is blue.

Now, we are inconsistent. Right? But if I am proven wrong i.e. the flower is not red, does that mean that you are correct i.e. the flower is blue? No. The flower could be pink or purple or any other color.

Thus, it is possible that though your answer is inconsistent with mine, it is also wrong.

Similarly, it’s possible that though Copernican theory is inconsistent with Ptolemaic theory, it is also false. However, the conclusion states that Copernican theory is true and thus the in-built assumption of the argument is that if two theories are inconsistent with each other, both of them cannot be false. 
 
With this understanding, let’s look at the option statements:
 
 A. whoever first observed something inconsistent with the truth of the Ptolemaic theory should be credited with having proved that theory is false 
 
This statement discusses who should be given the credit to prove that Ptolemaic theory is false. We are given Ptolemaic is false. Who should be given credit is not the focus of the argument. Thus, this choice is incorrect.
 
 B. there are some possible observations that would be inconsistent with the account given by the Copernican theory but consistent with the account given by the Ptolemaic theory 
 
This statements talks about the observations that would be inconsistent with Copernican theory but consistent with Ptolemaic theory. However, we are only concerned with Galileo’s observations in this argument, not other observations. Thus, this choice is an irrelevant and incorrect choice. 
 
 C. the Ptolemaic and Copernican theories, being inconsistent, cannot both be based on exactly the same evidence 
 
This statement is about the basis of both the theories; however, whether or not these theories are based on the same evidence, the conclusion of the argument is unaffected. In the argument, we are concerned about the impact of one set of observations on the truth of these theories; we don’t know the original basis of any of these theories. Therefore, basis of the theories is not relevant to the argument. Thus, this is an incorrect choice. 
 
 D. numerous counterexamples were necessary in order to show the Ptolemaic theory to be false 
 
We know from the passage that Galileo’s observations showed that the Ptolemaic theory is false This option tells us that it required numerous counter examples to show this result; however, our task is to look for the assumption that the argument makes while drawing the conclusion about the truthness of Copernican theory. Thus, this choice is incorrect.
 
 E. the Ptolemaic and Copernican theories, being inconsistent, cannot both be false  
 
This option identifies with our pre-thinking. The argument fails to consider that despite being inconsistent, both the theories can be false. This choice states the built-in assumption of the argument. 
 
If we negate this option we get,
the Ptolemaic and Copernican theories, being inconsistent, can both be false 
 
It shows that Copernican can be false, even if it is inconsistent with Ptolemaic theory. As we can see this breaks down the conclusion, this is the correct choice.

Ans is E.

Hope this helps!
Dolly

Beyond700 · Answer

between 'C' & 'D' 

As the quesiton looks at the argument I will go for 'D'

gregspirited · Answer

Neither is right according to OA. I went with C

parsifal · Answer

E.

While making the argument, the author assumes that if a theory is wrong, then any other inconsistent theory is right. It is however possible that 2 inconsistent theories are both wrong.

GMATBLACKBELT · Answer

E. lets say the theories can both be false, then the argument falls apart.

marcodonzelli · Answer

A theory is either true or false. Galileo’s observations of Jupiter’s satellites showed that the Ptolemaic theory of the motion of celestial bodies is false. Therefore, since the Copernican theory of planetary motion is inconsistent with the Ptolemaic account,Galileo’s observations of Jupiter’s satellites proved the truth of the Copernican theory.The argument above is open to the objection that it makes the questionable assumption 
that
A. whoever first observed something inconsistent with the truth of the Ptolemaic theory should be credited with having proved that theory false
B. there are some possible observations that would be inconsistent with the account given by the Copernican theory but consistent with the account given by the Ptolemaic theory
C. the Ptolemaic and Copernican theories, being inconsistent, cannot both be based on exactly the same evidence
D. numerous counterexamples were necessary in order to show the Ptolemaic theory to be false
E. the Ptolemaic and Copernican theories, being inconsistent, cannot both be false

Because Galileo's theory and Copernican theory prove that the Ptolemaic one is false, they are true. So, if the Ptolemaic theory is false, the Copernican one cannot be false as well. E is correct

bsv180985 · Answer

A theory is either true or false. Galileo's observations of Jupiter's satellites that the Ptolemaic theory of the motion of celestial bodies is false. Therefore, since the Copernican theory of planetary motion is inconsistent with the Ptolemaic account, Galileo's observations of Jupiter's satellites proved the truth of the Copernican theory.

The argument above is open to the objection that it makes the questionable assumption that

(A) whoever first observed something inconsistent with the truth of the Ptolemaic theory should be credited with having proved that theory false
(B) there are some possible observations that would be inconsistent with the account given by the Copernican theory but consistent with the account given by the Ptolemaic theory
(C) the Ptolemaic and Copernican theories, being inconsistent, cannot both be based on exactly the same evidence
(D) numerous counterexamples were necessary in order to show the Ptolemaic theory to be false
(E) the Ptolemaic and Copernican theories, being inconsistent, cannot both be false

PussInBoots · Answer

Looks like E to me

(e) => One of theories has to be right
Stimulus => One of theories is wrong, hence the other one is right

11MBA · Answer

E pretty easy. Just bc Copernicus's theory is inconsistent with Ptolemy's doesn't mean it's true.

akshathbs · Answer

use assumption negation that works..ans is E!

omidsa · Answer

I want to know the meaning of this statement....
"The argument above is open to the objection that it makes the questionable assumption that "
Should we look up for a false assumption? How could we do that?

aditya8062 · Answer

when they say that argument is wrong because of questionable assumption then we have to make that faulty link exposed .and thats exactly what E is doing .in simple terms what is argument saying ? lets say argument makes a claim that X is wrong then it says Y is inconsistent with X then it concludes that Y is right .what is wrong in this argument .that fact that it assumes that two inconsistent things cannot be wrong at the same time .this is what E talks

krrish · Answer

can u please post the answer over here??

my answer was C

mnm21234 · Answer

When Galileo's observation proved Ptolemic theory is false, why was the copernican theory automatically accepted? The passage is assuming that both theories cannot be false.

ozhan · Answer

Answer is E. Proving one theory wrong does not mean that every other theory incosistent with the first theory is true.

jlgdr · Answer

Anyone want to elaborate on what's wrong with C here? Thanks! Cheers J

GMATPill · Answer

Received a PM to chime in here:

Use linked chains to understand the logic and WEAKEN the argument. You WEAKEN the argument by identifying what the assumption is.

We have 3 things:
A) Galileo
B) Ptolemaic 
C) Copernicus

B = False

Passage says: Since B is bad and we know that C is not the same as B, then it must be that C is true.

Why is this argument flawed?

Just because C is not the same as B -- does not mean that C cannot ALSO be False. What if BOTH (B) and (C) were false? <<--that's the assumption

Assumption = anything that says C is similar to B. Or anything that says B and C cannot both be false.

If the assumption is wrong -- if it's actually possible for both B and C to be wrong -- then the author's whole argument falls apart.

So we look through the answer choice that says something along the lines of what we mentioned above.

(E) says what we want.

lakshey1993 · Answer

P1 :- Galileo proved ptolemaic theory false.

P2 :- Copernican theory inconsistent with ptolemaic

C :- Galileo observation proved truth of Copernican Theory.
th OA is E. Both theories might be inconsistent but we have no proof about either one to be considered false.

sowragu · Answer

A theory is either true or false. Galileo’s observations of Jupiter’s satellites showed that the Ptolemaic theory of the motion of celestial bodies is false. Therefore, since the Copernican theory of planetary motion is inconsistent with the Ptolemaic account,Galileo’s observations of Jupiter’s satellites proved the truth of the Copernican theory.The argument above is open to the objection that it makes the questionable assumption 
that

Meaning: Galileo Observation - Ptolemaic Theory false since its inconsistent with Copernican theory he concluded that the Ptolemaic Theory is false.
Pre thinking : Only when Copernican theory is true, We can say that Ptolemaic theory as false when its inconsistent.
The choice should answer the question : Y Ptolemaic theory was stated as false when compared to Copernican theory?

Choice analysis.
A. whoever first observed something inconsistent with the truth of the Ptolemaic theory should be credited with having proved that theory false
 The argument is not about whether Galelio should be credit or not instead it should answer why they Ptolemaic theory was stated as false. 
B. there are some possible observations that would be inconsistent with the account given by the Copernican theory but consistent with the account given by the Ptolemaic theory
 It weakens the argument. Hence eliminated. 
C. the Ptolemaic and Copernican theories, being inconsistent, cannot both be based on exactly the same evidence
 Only when something is false, we can say something as true. The above stated argument is Irrelevant 
D. numerous counterexamples were necessary in order to show the Ptolemaic theory to be false
 The argument is completely out of scope. Our answer choice should be in scope with comparison between Ptolemaic and Copernican theories 
E. the Ptolemaic and Copernican theories, being inconsistent, cannot both be false.
 This answer the question raised above or inline with the argument. Hence E.

A theory is either true or false. Galileo's observations of

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