A Post Hoc is a fallacy with the following form:
1. A occurs before B.
2. Therefore A is the cause of B.
There are also a few examples that help to understand this fallacy. Among these examples there is this one:
Bill purchases a new PowerMac and it works fine for months. He then buys and installs a new piece of software. The next time he starts up his Mac, it freezes. Bill concludes that the software must be the cause of the freeze.
I couldn’t help the smile. In the scope of logic as a science this example perfectly illustrates the point. But in the scope of computer science this quote would be a good example of the opposite. In other words, if you computer worked fine for months and than you installed a new piece of software on it, and it started to freeze – chances are that the software is the cause of problem.
Ironical, isn’t it?