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.
Constructivism is a theory of learning that is developed from the principle of children's thinking. Constructivism states that children learn through adaptation. Children are not passive in knowledge, but active at making meaning, testing out theories, and trying to make sense out of the world and themselves.