#26 - Current evidence indicates that there is no methane

[Administrator]

Please post your questions below! Thank you!

[theamazingrace]

I chose A for this question but I think it is wrong because it acts as a conclusion rather than an additional premise?

Planet 253 ---> no methane ---> no life on p 253
No methane ---> no microbes

D: No micobes ---> planet 253 ---> no methane ---> no life on planet 253

Is this correct?

[Adam Tyson]

Inserting "Planet 253" into the conditional chain is a bit confusing, theamazingrace. Your first diagram would read something like "If Planet 253, then no methane, and if no methane then no life." Your diagram of answer D reads as "If there are no microbes then it is Planet 253, and if it is Planet 253 then there is no methane, and if there is no methane then there is no life on Planet 253." That's odd, and also an incorrect interpretation of what that answer is doing. Take the planet out of the chain, because it is not a conditional element. It's just a place where these conditions occur.

The goal here is to prove the conclusion, which is that there is no life on that planet. The evidence presented is enough to allow us to infer that if there is no methane, then there can be no microbes, but that doesn't tell us anything about life. To justify a conclusion about life, we need to close the gap between "no microbes" from the premises and "no life" in the conclusion. We need an answer that says that if there are no microbes then there cannot be life, which answer D does. Here's how that might look:

Premise: It appears that there is no methane

Premise: Microbes always produce methane

Sub-conclusion: If there is in fact no methane, there are no microbes

Main conclusion: If there is no methane, there is no life

You can see how the first two premises do a good job of supporting the sub-conclusion here, but the main conclusion comes out of nowhere talking about life when we have zero evidence about life. We need a new premise between the sub-conclusion and the main conclusion that connects the absence of microbes to the absence of life. That's what we should prephrase, and what we should look for in the answer choices - a connection between microbes and life. Answer A is incorrect because it tells us nothing at all about life, and we are supposed to be proving the conclusion that there is no life.

Be careful about building conditional chains that are not based on "if this, then that" statements! Also, when faced with a Justify the Conclusion question, if the conclusion of the argument has some new, "rogue" element in it, be sure that your prephrase deals with that new thing and that you reject any answer that fails to connect to that new thing! You may be able to answer a question like this one with no diagram at all if you just take that mechanistic approach.

[lounalola]

I'm a bit confused about this one. Why isn't B correct and why is E the correct answer?

[Jeff Wren]

Hi lounalola,

The first step in analyzing the argument in the stimulus is to correctly identify the conclusion of the argument and to note whenever a new term/concept/idea appears in the conclusion. Whenever there is a new term/concept in the conclusion, this creates a logical gap in the argument that is often the key to solving the question, especially in Justify the Conclusion questions like this one.

Here, the conclusion is the second sentence. It is the statement that everything else in the argument supports. This conclusion mentions the idea of "no life" on Planet 253. The idea of "no life" does not appear anywhere in the premises, so there is a logical gap in the argument. The premises do mention "no microbes," but "no microbes" do not necessarily mean "no life." For example, there may be life other than microbes on Planet 253 for all we know.

Because we need an answer that must 100% prove our conclusion regarding "no life" on Planet 253, any answer that doesn't mention "life" or "no life" (or something synonymous) cannot prove this conclusion and will be wrong. (The reason I include "life" as well as "no life" is that the answer can just use the word "life" depending on how it is worded, such as using the contrapositive.)

Answer B doesn't mention "life" or "no life," so it does not justify our conclusion and is wrong. (This is also true of Answers A and C.)

You are right to note that the fact that current evidence indicates that there is no methane doesn't actually prove that there is in fact no methane, which is what Answer B addresses. However, this isn't a problem for the argument because the conclusion stipulates "if that is the case" meaning if the evidence is correct that there is in fact no methane. Since this is already accounted for in the conclusion, it does not need to be addressed in the answer choice.

Instead, what the correct answer choice needs to do is to link no microbes to no life, which is exactly what Answer D does. If you add Answer D to the premises of the argument, you 100% prove/justify the conclusion.

Premise: Evidence indicates no methane.
Premise: If no methane, no microbes.
Answer D: If no microbes, no life.
Conclusion: If evidence (that there is no methane) is correct, then no life.

Answer E does mention "life," but this answer is actually a Mistaken Negation of our conclusion and therefore does not justify the argument. We are trying to justify the conclusion: if no methane, then there is no life. This answer states: if there is methane, then there is life.