Ad hoc hypothesis

In science and philosophy, an ad hoc hypothesis is a hypothesis added to a theory in order to save it from being falsified.

For example, a person that wants to believe in leprechauns can avoid ever being proven wrong by using ad hoc hypotheses (e.g., by adding "they are invisible", then "their motives are complex", and so on).^[1]

Often, ad hoc hypothesizing is employed to compensate for anomalies not anticipated by the theory in its unmodified form.