This topic is, I think, most succinctly explained in Isaac Asimov&#x27;s <i>The Relativity of Wrong</i>[1]. These concepts which rely on categories that you describe are wrong, but they&#x27;re far less wrong than many other ideas. Don&#x27;t forget that often science is used for prediction, and for prediction a good approximation is very useful. Yes, Tasmanian devils are a counterexample to the idea that cancers are never communicable, but it&#x27;s an extremely rare counterexample. One can achieve great results in the study of cancers based on the assumption that cancers are never communicable.<p>[1] <a href="http:&#x2F;&#x2F;chem.tufts.edu&#x2F;AnswersInScience&#x2F;RelativityofWrong.htm" rel="nofollow">http:&#x2F;&#x2F;chem.tufts.edu&#x2F;AnswersInScience&#x2F;RelativityofWrong.htm</a>