I tried googling my last two posts on errors in reasoning, and discovered that many, many blog posts exist out there accusing the Bible, and therefore Christianity, of being full of these fallacies. But after reading a few of them, I realized that the problem is that many Christians don't understand (or don't bother with) good debate technique. If you're sharing your faith with an unbeliever, it is absolutely essential that you understand these fallacies, and don't use them. If what you have to say is really defensible, you don't have to trick people into believing it.
So, on to the next fallacy...
Superstition or Bad Science: Post Hoc, Ergo Propter Hoc
With such a long handle on this one, you would think it would be something really clever, but I honestly think its one of the easiest to identify. Post Hoc, Ergo Propter Hoc is a really fancy, Latin way of saying, After this, therefore because of this. I think of it as the superstitious or bad science argument, because it is based on the illogical idea that because something follows something else, it must be the result of the first occurrence. The definition of good scientific reasoning is that the results are repeatable, explainable, unbiased, and so forth. Superstitious assumptions do not hold up under such scrutiny.
A common quasi-religious example is the notion that if you spill salt, you are doomed to bad luck unless you throw some over your shoulder. Honestly, it cannot be proven that spilling salt was the origin of all the bad things that happened to you. It could be that you didn't get enough sleep, and therefore had sluggish reflexes that day, which caused you to dump the salt and wreck your car in the same day. It also cannot be proven that throwing salt over your shoulder reverses the trend.
The worst thing about the Post Hoc argument is that it causes you to overlook better explanations for what happened, and may prevent others from looking for them, as well.
Example: "But when he saw many of the Pharisees and Sadducees coming to where he was baptizing, he said to them: "You brood of vipers! Who warned you to flee from the coming wrath? Produce fruit in keeping with repentance. And do not think you can say to yourselves, 'We have Abraham as our father.' I tell you that out of these stones God can raise up children for Abraham." (Matthew 3: 7-10 NIV).The speaker is John the Baptist. The Post Hoc argument is that because we were born Israelites, we are holy, like Abraham was holy, and children of the promise God made to him to bless his descendants. But John is saying, holiness results from repentance, not from being born into a family.