#23 - Linda says that, as a scientist, she knows that no

[Jeff Wren]

Hi maeve,

This question (and my explanation) involves formal logic. For more information on formal logic, check out chapter 13 of "The Logical Reasoning Bible."

First, let's examine the stimulus to determine what exactly the flaw in the argument is.

You correctly diagrammed the premises of the argument.

Scientists (crossed out) Appreciates Poetry
Scientists Logical

While "most" is not reversible, "most" includes the inherent inference "some," which is reversible, so we know that:

Scientists < some > Logical

We can the combine our "some" statement with our "no" statement in one diagram, placing our linking term "scientists" in the middle:

Logical < some > Scientists (crossed out) Appreciates Poetry

Using the "some train" (as described in the "The Logical Reasoning Bible), the inference that we can logically make is:

Logical < some > (crossed out) Appreciates Poetry

In plain English, this means that some logical people do not appreciate poetry.

However, the actual conclusion states that some people who appreciate poetry are illogical, which would be diagrammed:

Appreciates Poetry < some > (crossed out) Logical

Hopefully you spot the crucial difference in which term is positive and which term is negative. This conclusion is not valid based on the premises.

Answer B contains the exact flaw as the stimulus, which is why it is the correct answer.

You correctly diagrammed the premises.

Fathers (crossed out) Wants children eat candy before bedtime
Fathers Adults

From the "most " statement, we get:

Fathers < some > Adults

Rearranging the terms we get:

Adults < some > Fathers (crossed out) Wants children eat candy before bedtime

The correct inference should be:

Adults < some > (crossed out) Wants children eat candy before bedtime

In plain English, this means that some adults do not want children to eat candy before bedtime.

However, the actual conclusion states that some people who do want children to eat candy before bedtime are not adults (i.e. children), which would be diagrammed:

Wants children eat candy before bedtime < some > (crossed out) Adults

(Note that it's important to diagram "children" as "not adults" to correctly match up the terms/logic with the stimulus).

Answer A does not contain this flaw and is in fact a valid argument using the "some train."

Using

Native Australia < some > Marsupials (crossed out) Lays Eggs

We can infer:

Native Australia < some > (crossed out) Lays Eggs

which is what the conclusion of Answer A correctly states.