Logical reasoning PrepTest 127 · Section 1 · Question 14

Flawed

Errors in Reasoning Questions

People with significant brain damage show no effects, so almost all of the brain does nothing, and once we tap into this source of creativity/innovation, we can solve many problems.

This argument starts with a common piece of (incorrect) pop knowledge - 90% of the human brain does nothing. This is some type of conclusion since the following statement starts with a premise indicator - “as is evident from the fact.” After that line, the argument then goes on to another conclusion, so we have a premise-intermediate conclusion-main point structure. Looking at the two conclusions, we can see that the opening line supports the last line (not well, but that’s the direction of the logic). We need to analyze each step to see if there’s an error in reasoning there.

Let’s start with the premise to intermediate conclusion. If people with brain damage show no discernible adverse effects, does that guarantee most of the brain does nothing? It does not - maybe those parts of the brain are backups, and so they can be knocked offline without discernible effects until a “tipping point” is reached. Or maybe they do things that we can’t yet monitor, thus making the effect indiscernible. Any answer highlighting this jump would describe an error in reasoning.

Now, looking at the intermediate conclusion to main point jump, is there an assumption there? Yep - that the 90+% of the brain that serves no purpose is a potential source of creativity and innovation. Maybe it’s just useless mush, an evolutionary relic that can’t serve any purpose. This is another jump that the correct answer might bring up, so we’ll need to look for both.