#7 - Failure to rotate crops depletes the soil's nutrients

[ncolicci11]

Powerscore,

Just so I am understanding the process of approaching the question, is the following chain an accurate idea of what we are looking for in the answer?

Negated F ----> Negated AC ----> Negated D----> RC or PM

So, because our question stem indicates they were not fertilized, we are looking for something that must be true along this chain?

Also, how commonly does the twist to the unless equation appear on tests?

[Adam Tyson]

That chain doesn't look quite right to me, ncolicci11. I would read what you wrote like this:

If no fertilizer is used, then additional crops cannot be grown, and if additional crops cannot be grown, then the soil is not depleted, and if the soil is not depleted than we must have rotated crops or else taken other preventative measures.

This is not quite what the stimulus is saying. It's "if you don't use fertilizer AND the soil is depleted, then you cannot grow additional crops." And as to the soil being depleted, it's saying "if you don't rotate crops and if you do not take other preventative measures, then the soil will eventually become depleted." It's not a straight line, but a bunch of multi-conditionals and nested conditionals.

Focus on the information in the stem - we are able to grow crops without using fertilizer. What does that mean? Well, since you cannot grow stuff in depleted soil without fertilizer, and we are growing stuff without fertilizer, then the soil must not be depleted yet. It still has at least some nutrients in it. Find that in the answer choices and you will have your winner! We cannot know why the soil is not depleted - maybe crops were rotated, or many other preventative measures were taken - but we know for sure that the nutrients in the soil are not depleted.

Those multi-conditionals and nested conditionals can be a real bear to deal with, and that use of "unless" to create them is common enough that you should study it carefully. I think there is a good chance that one LR question on your test will have that level of complexity, probably late in the section, and it will be crucial that you diagram it correctly. Keep at it, you'll get there!

[MayaPapaya]

Hi!

I would just like to clarify how the diagram of the first sentence was done through verifying a principle that seems to be giving me trouble on this question as well as 17 in this same section. I have reviewed the LR Bible as well in search of this, so please let me know if I missed discussion of this.

We diagram the first sentence: ~RC + ~PM --> D.

Is this because we are combining ~RC --> D with ~PM--> D ? I know this is quite basic but I can't find confirmation if this is correct in formal logic.

This same principle trips me up in 17, with the final conditional that is basically IF A + B <--some--> C +D; how can we infer from this that some A are D (and basically ignoring B and C)?

Essentially, my issue is splitting up or putting together these "AND" statements. Thank you in advance!!

[MayaPapaya]

Hi!

I would just like to clarify how the diagram of the first sentence was done through verifying a principle that seems to be giving me trouble on this question as well as 17 in this same section. I have reviewed the LR Bible as well in search of this, so please let me know if I missed discussion of this.

We diagram the first sentence: ~RC + ~PM --> D.

Is this because we are combining ~RC --> D with ~PM--> D ? I know this is quite basic but I can't find confirmation if this is correct in formal logic. I thought we could only do this with OR statements.

This same principle trips me up in 17, with the final conditional that is basically IF A + B <--some--> C +D; how can we infer from this that some A are D (and basically ignoring B and C)? Here, I also thought we can only do this if they were OR statements.

Essentially, my issue is splitting up or putting together these "AND" statements. Thank you in advance!!

[KelseyWoods]

Hi Maya!

We can't separate the statement RM + DM D into two statements: RM D and DM D. The basic rule for separating statements that have multiple sufficient or necessary conditions is that you can separate them if the OR is at the beginning of the arrow or if the AND is at the end of the arrow. But we can't separate them when the AND is at the beginning of the arrow (as we have in this question) or when the OR is at the end of the arrow.

To diagram the first sentence, we need to really think about what it actually means: “Failure to rotate crops depletes the soil’s nutrients gradually unless other preventive measures are taken.” What is that really saying? It's saying that if we fail to rotate crops, then it's going to deplete the soil, unless we take preventive measures. So what would ensure that the soil will be depleted? If we fail to rotate crops AND we don't take other preventive measures. In other words, if we don't rotate the crops and if we don't take other preventive measures, then the soil will be depleted.

When you're struggling with a conditional statement, really try to think about what the statement is actually saying. Sometimes it helps to try to rephrase it in if/then terms.

Hope this helps!

Best,
Kelsey