Fallacy of the Week #1

To follow up from the previous post concerning the value of "natural"ness, I'd like to talk a little bit about the genetic fallacy.

Put simply, you're committing a genetic fallacy when your argument is that a thing is good now because it was good before or had its origins in something good. An example might be a claim like

I know that Jack is a good person because I know his parents, and they're good people.

Of course, we can use predicates other than "good" and still be committing a genetic fallacy, e.g:

NaCl (table salt) is poisonous because Na is poisonous and Cl is poisonous.

It's important to keep in mind that this is a claim about knowledge (how I know that something is the case) and not one about causes (why something is the case). The examples provided in the Wikipedia article linked to above are pretty clear cut, but many instances of this fallacy in our everyday lives are more ambiguous. 

It feels silly and unnatural to us to disclaim our statements as being about knowledge as opposed to causes, so that's something we have to keep an eye out for, not to mention the fact that we often make claims about causes and knowledge simultaneously, as if they were the same thing. We ought to be especially vigilant because it is often the case, as with our friend Jack above, that the claim about causes has merit (it is not unreasonable to claim that being raised by good people causes you to be a good person) while the claim about knowledge does not (it is unreasonable to claim that we have knowledge of a person's goodness based on knowledge of his/her parents' goodness, unless we've already accepted the validity of the causal claim).

In the claim that a thing is bad because it is "unnatural," a reverse genetic fallacy is being committed:

X is bad because it does not have its origins in Y, and Y is/was good.

X is good because it does not have its origins in Y, and Y is/was bad.

A very obvious example of why this is usually a bad plan:

Murder is good because it does not have its origins in Nazism, and Nazism was bad.

And a slightly less obviously example:

Homosexuality is bad because it does not have its origins in nature, and nature is good.

Bear in mind that because genetic fallacies are informal (that is, their form sends up a red flag to reevaluate their merits, but does not automatically disqualify the conclusions), the conclusions they lead to are not always wrong:

This mixture of cyanide and arsenic is poisonous, because cyanide is poisonous and arsenic is poisonous.