Ad hoc is a Latin phrase meaning "for this". In English, it generally signifies a solution designed for a specific problem or task, non-generalizable, and not intended to be able to be adapted to other purposes.
In science and philosophy, ad hoc means the addition of extraneous hypotheses to a theory to save it from being falsified. Ad hoc hypotheses compensate for anomalies not anticipated by the theory in its unmodified form. Scientists are often skeptical of theories that rely on frequent, unsupported adjustments to sustain them. This is because, if a theorist so chooses, there is no limit to the number of ad hoc hypotheses that they could add. Thus the theory becomes more and more complex, but is never falsified. This is often at a cost to the theory's predictive power, however. Ad hoc hypotheses are often characteristic of pseudoscientific subjects.
Ad hoc argumentation is not a logical fallacy, but Occam's razor is the problem-solving principle that, when presented with competing hypothetical answers to a problem, one should select the answer that makes the fewest assumptions.
Ad hoc arguing is often used by race denialists. One example is when blaming politically incorrect race differences on certain politically correct factors, such as poverty and racism afflicting non-Whites. After being informed that East Asians in Western countries on average have good outcomes, despite previous poverty and racism, race denialists may attempt ad hoc arguing in order to save their theory.
- Differential K theory - Argued to be a simpler theory than many ad hoc non-genetic explanations for various racial differences.