Affirming the consequent: a logical fallacy

Affirming the consequent: a logical fallacy

By Riaan Visser (from FB post)

Affirming the consequent, sometimes called converse error, fallacy of the converse, or confusion of necessity and sufficiency.

This is a fallacy where a conditional statement is made and it's converse is invalidly inferred.

This argument of fallacy takes the following form:

If X then Y

Y is true

Therefore X is true

Example:

P1 "If my car has no fuel, it will not start"

P2 "My car won't start"

Conclusion "My car has no fuel"

This reasoning excludes all other possibilities, the engine might be broken, while you're fuel tank is full for instance.

The following statement is commonly accepted as fact by evolutionists.

P1 "If life is related, it will have common genetic code"

P2 "We find common genetic code"

Conclusion "All life is related"

Let's examine the premises and then the conclusion.

P1 is true

P2 is true

But the conclusion that therefore all life is related is not the only explanation to the common code, this is affirming the consequent.

And is not a valid form of argument, but is in fact a fallacy. Note I do not even need other explanations. The logical form of the argument is invalid, and therefore a fallacy.

--> "So the evolutionary claim that because all life shares a common code, therefore all life is related is based on a fallacy, and is therefore not scientific."

But here are some alternative explanations for the sake of being engaging. The fallacy of the argument however cannot be avoided by simple hand waving.

a) common code denotes common language, and not common ancestry. All computers run in binary code. But there's multiple companies that make computers, neither the computers or the companies share a common ancestor.

b) The English language is also a code, using 26 letters. Many books have been written in English, yet none of them share a common ancestor. Even my mother tongue Afrikaans has the exact same 26 letter alphabet as English. But again the two languages don't share a common ancestor.

Other explanations for common code found in genetics:

1) There is no other code for life, so any life that might arise will inevitably be comprised of the same code.

2) Common code denotes common function. Ie. Using oxygen would require the same code across all organisms that use oxygen.

***

Possible Objections:

A)"Junk DNA has no function yet there are still similarities found."

Response: the function of so called junk DNA is ever more understood as our knowledge increases. Our known limited knowledge cannot claim junk DNA has no function, as the assumption is based on our limited knowledge.

B)" Retro viruses leave genetic markers indicating common ancestry."

Response: retro viral infections would by definition leave the same genetic alteration in the same functioning code and does not denote common ancestry. Many retro viruses are essential to life, common retro virus infection indicates again common function.

C) "you don't understand genetics" 

Response: avoiding the argument.

D) "most scientists accept common ancestry"

Response: fallacy of appealing to authority.

C) "you're an idiot"

Response: Possibly, but I'm not the one who accepts unfalsifiable arguments of fallacy as science"

D) "evolutionary theory is fact"

Response: theories are never fact, they can only ever be supported by observational evidence, which evolutionary theory is not.

E) "nah nah nah boo boo your belief is doo doo"

Response: thanks for conceding the argument. 

Have a nice day!