"The trees always blossom in May if April rainfall exceeds 5 centimeters."
PR1: AR>5 ==> TBM
not TBM ==> not AR>5
"April rainfall exceeds 5 centimeters, then the reservoirs are always full on May 1."
PR2: AR>5 ==> RFM1
not RFM1 ==> not AR>5
"The reservoirs were not full this May."
P: not RFM1
"Thus the trees will not blossom this May."
C: not TBM
The flaw is that we are concluding "not TBM" from "not RFM1," when all we can deduce from "not RFM1" is "not AR>5."
"Not AR>5" is the necessary condition for the contrapositive of the first principle rule; so we cannot conclude anything further.
Rather, the argument is using the necessary condition "not AR>5" to conclude the sufficient condition "not TBM."
Compare that with (E):
"If the kiln is too hot, then the plates will crack."
PR1: KTH ==> PC not PC ==> not KTH
"If the plates crack, then the artisan must redo the order."
PR2: PC ==> RO not RO ==> not PC
"The artisan need not redo the order."
P: not RO
"Thus, the kiln was not too hot."
C: not KTH
This is a valid contrapositive argument that using the following contrapositive transitive chain:
not RO ==> not PC ==> not KTH
So (E) would be eliminated since it is not flawed and it does not exhibit the same pattern of reasoning.
Hope that helps! Please let us know if you have any other questions.
rexcolemanSeptember 25, 2017
Hello. Will you explain why answer choice "D" is not the answer?
MehranSeptember 28, 2017
Hi there, thanks for your post.
In the stimulus, the conclusion is (not) TBM. This is flawed reasoning, because the argument uses the necessary condition "not AR>5" to conclude a sufficient condition "not TBM."
Ok. Now let's examine answer choice (D):
Premise 1: The mower will operate only if the engine is not flooded.
MO ==> not EF
CP: EF ==> not MO
Premise 2: The engine is flooded if the foot pedal is depressed. [If marks the sufficient condition:]
FPD ==> EF
CP: not EF ==> not FPD
Premise 3: The foot pedal is not depressed.
not FPD
Conclusion: So the mower will operate.
MO
This, too, is flawed, but for a different reason than the flaw in the stimulus.
In answer choice (D), you are told that the foot pedal is not depressed (not FPD). Where do we see this? In the contrapositive of the second given premise: not EF ==> not FPD. Because (not FPD) is on the necessary side, we cannot conclude anything further from the fulfilment of this condition (not FPD; that is, from Premise 3).
Yet answer choice D then concludes that the sufficient condition of the FIRST premise (MO) will be fulfilled. This is logical error, but a different logical error than that in the stimulus.
Hope this helps! Please let us know if you need any additional assistance.
