#14 - The axis of Earth's daily rotation is tilted with

[Eric Ockert]

Hi again!

The difference between answers (A) and (B) really comes down to sufficient versus necessary. The stimulus tells us that life needs a stable and moderate axis tilt (the use of the word "without" in the stimulus conveys this necessity). It also tells us that the stable axis needs the large, nearby moon. So we can diagram these relationships accordingly:

Climate that supports life Stable and moderate axis Large nearby moon

The contrapositive of this chain tells us that if you don't have a large nearby moon, then you won't have a stable axis, and if you don't have that stable axis, you can't have a climate that supports life. This is essentially what answer choice (B) says. If Earth had no moon, it couldn't support life.

Answer choice (A) is attempting to claim what amounts to a Mistaken Reversal. It is saying if Mars did have a large moon, then it would be able to support life. That, like all Mistaken Reversals, does not have to be true.

Hope that helps!

[Stephanie Oswalt]

We received the following question from a student. An instructor will respond below. Thanks!

Hi,

My stimulus diagram is correct and I also put the correct answer. I had a question about the role of the last sentence in the fact set and answer choice (A). Is the example of Mars used as a contrast with Earth's large moon or is it a distractor element?

I eliminated (A) for two reasons: 1) since this is a MBT question I need to find an answer that fits with the criteria from the previous chapter. So, I interpreted this answer choice as a scenario that was not stated in the stimulus; 2) even if Mars had a large moon there are other reasons that it would be unable to support life such as lack of water but now I am thinking I brought outside knowledge into the question and this doesn't reflect what the author said.

After reading the answer choice analysis I tried to diagram (A), but I diagrammed it wrong.

My diagram (A):

GIM PCEM

I don't understand why the second element is negated. If anything, I thought both elements would be negated because Mars doesn't have a large moon, and without a large moon there would be less gravitational influence for a stable angle so life cannot be supported.

Also, I eliminated (C) and (E) because of the strong phrasing, but I think that is dangerous. I thought "any" was too strong for (C) since the stimulus focuses on Earth and then Mars. I eliminated (E) because of the "no" and also because the stimulus did not bring up the idea of a planet having more than one moon that can support life. It only discussed Earth with one large moon, and Mars which has small moons. Thus, combining those two ideas together seemed incorrect.

Lastly, is the last sentence able to be diagrammed?

Thanks!
SA

[Francis O'Rourke]

The last sentence was largely irrelevant to getting at the correct answer. We can think of it as a clarification for the preceding sentences, but for most people it will probably function as a distraction.

I would not diagram this sentence, since there is no necessary connection expressed in it.

even if Mars had a large moon there are other reasons that it would be unable to support life such as lack of water but now I am thinking I brought outside knowledge into the question and this doesn't reflect what the author said.

That's great reasoning! It is not bringing in outside knowledge to say that there may be other factors at play. If the speaker tells you that a condition is necessary for something else, it is completely appropriate to remember that it may not be sufficient.

My diagram (A):

GIM PCEM

I don't understand why the second element is negated.

Unfortunately I am unable to follow what you are referring to here. Can you try rewriting and explaining this part of your question?

I thought "any" was too strong for (C) since the stimulus focuses on Earth and then Mars. I eliminated (E) because of the "no" and also because the stimulus did not bring up the idea of a planet having more than one moon that can support life. It only discussed Earth with one large moon,

That's exactly correct!

[Tyiop157]

Hi,

I was doing this question and I got it right, but my diagramming and the books diagramming are not the same. I’ve tried over and over but I can’t seem to get the diagramming that the book gets. This is my diagramming:

GIM - Gravitational Influence of the Earth’s large, near Moon
AS - Angle Stable
SL - Climate too extreme to support life

Therefore,

1) AS —> GIM
GIM/ —> AS/

2) GIM/ —> AS/ —> SL/
SL —> AS —> GIM

In the book this is the diagram (I’ll replace their legend with min to make it easier to follow)

AS = AS
GI = GIM
PCE = SL

Their Diagram:

1) PCE/ —> AS —> GI OR with my terms SL /—> AS —> GIM

2) GI/ —> AS/ —> PCE CONTRAPOSITIVE with MY TERMS GIM/ —> AS/ —> SL

Any clarity would be greatly appreciated, thanks!

[Robert Carroll]

Tyiop,

It looks like the issue with your diagramming is an erroneous application of the Unless Equation to the third sentence.

"Without" is an Unless Equation indicator, so "stable and moderate axis tilt" is necessary. The other component of the sentence must be negated to become the sufficient condition. Putting that together:

planet's climate too extreme stable and moderate axis tilt

In the abbreviations you've used:

SL AS

Robert Carroll

[Tyiop157]

Hi Robert,

Thanks a lot for your reply, this cleared it up a little bit I’m still a bit confused. Isn’t sentence 3 saying the sufficient condition is essentially “unstable to support life”, if this is a part of the unless/without equation, then shouldn’t this now be negated. Therefore, shouldn’t the end result of the sufficient condition be “(able to) support life (SL)”. Which still leads me to the equation I initially got? Thanks!

[Robert Carroll]

Tyiop,

Here is how you chose to define your abbreviations:

SL - Climate too extreme to support life

Given that, my diagram is accurate.

I think that abbreviation was not felicitous and that that is causing the confusion - things that are negative should probably be abbreviated so that the abbreviation is a positive statement and the abbreviation is negated symbolically. This has less potential for confusion. "SL" is actually already negative, given the way you stipulated it.

Robert Carroll

[abtinghz]

I have a question regarding the conditional reasoning diagram for the practice question on the bottom of page 212 of the LR self study bible.
the third sentence of the stimulus states "Without such a stale and moderate axis tilt, a planets climate is too extreme and unstable to support life".
the answer guide however, has drawn the correct diagram of the stimulus, with PCE (PCE=planets climate too extreme and unstable to support life) being the sufficient condition, however cancelled out by a line dragged across of it.
the question I have is regarding the cancellation of PCE, as on the stimulus it does not indicate that PCE is to be cancelled. Instead the stimulus states " Without such a stable and moderate axis tilt.." wouldn't that mean that one would have to cancel out "stable and moderate axis tilt"? why is PCE the condition that has been canceled out?
ID appreciate your response.

[abtinghz]

Complete Question Explanation

Must be true. The correct answer choice is (B)

The two sentences produce the following conditional relationships, which can be linked:


AS = angle stable
GI = gravitational influence of Earth’s large, nearby Moon
PCE = planet’s climate too extreme and unstable to support life

Sentence 2: AS GI
Sentence 3: PCE AS
Chain: PCE AS GI


Again, consider the answers that are most likely to appear in a problem like this: either the chain inference PCE GI, or the contrapositive of that chain inference, GI PCE.

Answer choice (A): This incorrect answer is the Mistaken Reversal of the chain inference. The diagram for this answer choice would be as follows, with the sub-M indicating Mars:


GIM PCEM


Answer choice (B): This is the correct answer. As expected, this is the contrapositive of the chain inference.

Answer choice (C): This incorrect answer is the Mistaken Reversal of the third sentence, and is diagrammed as follows:


AS PCE


Answer choice (D): This answer discusses issues that were not raised in the stimulus, and is thus incorrect.

Answer choice (E): The stimulus indicates that Earth’s large Moon has been necessary for the stable angle of Earth’s tilt, and this stable angle has been necessary for a climate that can support life. Mars, with many small moons, tilts at fluctuating angles and cannot support life. The key difference is that Earth’s Moon is large, and that creates a greater gravitational influence. It is possible, therefore, that a planet with more than one moon could have a stable angle as long as at least one of the moons was of sufficient size (in Mars’ case, the stimulus indicates each moon is small). Thus, it is possible that a planet can have more than one moon and support life. This scenario is contrary to the answer choice, and thus this answer is incorrect.

Note, this question appears in the Logical Reasoning Bible, and thus it has also been discussed multiple times on this Forum. For further discussions, please visit:

lsat/viewtopic.php?t=27721

lsat/viewtopic.php?t=10839

lsat/viewtopic.php?t=1868

lsat/viewtopic.php?t=28794

Ok so a few questions regarding you answer. Isn't "without" an indicator of a necessary condition? in which the remaining terms are negated and then become the sufficient condition? if so, why is PCE diagrammed as the sufficient component? Also, the last sentence also has a necessary indicator where it says "Mars, for example, has ONLY very small moons, tilts and wildly fluctuating angles, and cannot support life" But that seems to have been left out of diagraming as well.
Thank you for your initial response however. I greatly appreciate it.

[katehos]

Hi abtinghz!

Thanks for your questions! You're correct, "without" is an indicator of a necessary condition! When we see the word "without", we utilize the Unless Equation. In this equation, one takes the steps you mentioned, which are to make the term modified by "without" the necessary condition, then negate the remaining term and make it the sufficient condition. Thus, we can see why PCE is the sufficient condition; the phrase "stables and moderate axis tilt" becomes the necessary condition since it is modified by "without" and the remaining part of the phrase "planet's climate is too extreme and unable to support life" is negated (becoming PCE) and becomes the sufficient condition. This gets us the same diagram as mentioned in the quoted comment!

Regarding the last sentence, while you're correct that "only" can be an indicator, there's no conditional logic in the last sentence as there is no connection to another condition. Additionally, it's not relevant to the answer so it's unnecessary to diagram!

I hope this helps
Kate