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the following is from a flaw question on seven sage...
Theorist: To be capable of planned locomotion, an organism must be able both to form an internal representation of its environment and to send messages to its muscles to control movements. Such an organism must therefore have a central nervous system. Thus, an organism incapable of planned locomotion does not have a central nervous system.
Correct Answer
a
confuses a necessary condition for an organism's possessing a capacity with a sufficient one
My attempt to identify conditionals (May be False)
( Sufficient condition) be capable of planned locomotion. (Nessesary Condition indicated by must)
an organism must be able to both to form an internal representation of it's environment
and to send messages to its muscles to control movement.
but then what confuses me is what appears to be be another Necessary condition introduced in the subsequent sentence... "Such an organism must therefore have a central nervous system" again another must indicating what appears to be another Necessary condition. Then strangely the argument denys the antecedent aka the sufficient condition when it states " thus an organism incapable of planned locomotion, does not have a central nervous system.
I though confusing the sufficient and necessary condition is exactly like affirming the consequent
A>B
B
therefore A.
Logically valid structure
A>B
A
Therefore B..........
0
2 comments
I think that this is an illegal negation aka sufficient-necessary reversal.
This is how I mapped it:
if planned locomotion --> internal representation and send messages --> central nervous system
This is the conclusion made in the argument:
if /planned locomotion --> /central nervous system
Or:
if A --> B --> C
---------------
/A --> /C
This is an illicit conclusion because the conditions are not switched. The correct conclusion would be /C --> /A, or that if an organism does not have a central nervous system, then it is not capable of planned locomotion.
When you are taking the contrapositive of an argument, you must negate and swap the conditions.
A --> B
/B --> /A
If you don't negate:
B --> A
Or if you don't swap:
/A --> /B
Then you are confusing sufficient-necessary conditions.
Hope that helps!