On day 49 I discussed what post hoc ergo propter hoc meant: it’s an informal fallacy that claims that correlation proves causation, such as a roster crows, then the sun rises — therefore the rooster crowing makes the sun rise.

Cum hoc ergo propter hoc sounds similar to post hoc — it is also a false cause fallacy. However, cum hoc involves the claim “with this, therefore because of this”.

One example of this fallacy occurring is the claim that vaccines administered to children causes autism. The first signs of the developmental condition of autism is around 15 to 18th months of age, while vaccinations for preventable diseases such as measles, mumps and rubella are given around the same time.

Numerous studies into both vaccines and autism demonstrate that there is no causal link between the two — and yet, there are some people who propose that because vaccinations are given to infants within the time that autism can be identified… then ‘with this, therefore because of this’.

This particular example of the fallacy being applied is a serious concern for public health, since vaccinations help community immunity and the opportunity to prevent succeptibility to life-threatening diseases not only to children but to others.