A trick to using malapropism is to ensure that the two words (the original and the substitute) sound similar enough for the reader to catch onto the intended switch and find humor in the result.
Positivism is a philosophical theory stating that positive knowledge is based on natural phenomena and their properties and relations. Thus, information derived from sensory experience, interpreted through reason and logic, forms the exclusive source of all authoritative knowledge.
The roots of Positivism lie particularly with Empiricism, which works only with observable facts, seeing that beyond this is the realm of logic and mathematics. The basic principle of Positivism is that all factual knowledge is based on the positive information gained from observable experience, and that any ideas beyond this realm of demonstrable fact are metaphysical. Only analytic statements are allowed to be known as true through reason alone.