Logic Reasoning Set #3 Q 270

[Jkjones3789]

I am having some difficulty solving these Assumption questions mechanistically by finding the "missing link" between the premise and the conclusion. So could you assist me with solving this mechanistically.

No mathematical proposition can be proven true by observation. It follows that it is impossible to know any mathematical proposition to be true.

MP --> -PBTO

????? Thank you

[Lucas Moreau]

Hello, Jkjones,

I am glad that your first instinct is to diagram these questions! For Assumption questions, though, another type of diagram may be more effective. This is what I teach in the Weekend and Full-Length Courses I've done in the past.

An assumption is simply an unstated premise. Therefore, an Assumption question will contain some amount of premises and a conclusion in its stimulus, and the correct answer choice will contain the unstated premise that completes the argument. For this question, think of it like this:

P1: No MP can be PTBO
P2: ???
C: No MP can be known to be true

P2 is our missing premise, which must therefore be the correct answer choice. In this case, you're trying to link together "can be PTBO" with "can be known to be true". Looking at answer choice E lets us bring in the following to the diagram:

P1: No MP can be PTBO
P2: No thing that is not PTBO can be known to be true
C: No MP can be known to be true

That is a rephrasing of answer choice E, but it fits the diagram a little better. Often tricky phrasing will be the major source of difficulty in questions like these - learning to restate sentences in more clear language is a super useful skill!

As you can see, the argument is now logically sound. If no MP can be PTBO, and something must be PTBO to be able to be known to be true, then no MP can be known to be true. None of the other answer choices complete the argument so neatly.

Almost all Assumption questions can be answered this way. Practice if you like!

Hope that helps,
Lucas Moreau

[Jkjones3789]

Thank you so much. I am currently taking the full length course in NY but I need to perfect my Assumption questions. The way you diagrammed was very clear, I have one question though, why is that superior to writing it out as a conditional statement?

[Robert Carroll]

Jk,

Because the answer to an Assumption is, as Lucas explained, an unstated premise, diagramming the premises and conclusion, and leaving a gap where the missing premise is, allows you to put all the premises and conclusion in order, and see what's missing to complete the argument by proving the conclusion at the end.

Robert Carroll