Article: “What Happens if a Child Is Never Exposed to Language?”
“Children learn the language(s) that they hear and see around them at a young age, but what happens if a child just never has any linguistic input, spoken or signed? Although a scientific study around this question would undoubtedly be fascinating, it would also be extremely unethical, so much so that the cultural historian Roger Shattuck has called it The Forbidden Experiment.” https://slate.com/human-interest/2014/07/children-not-exposed-to-language-nicaraguan-sign-language-wild-children-and-the-forbidden-experiment.html
This real life example adds an ethical angle to prescribed title #6. There are experiments that can be done (such as the one in the article) that would make knowledge more certain. For ethical reasons however, some experiments are not done but the knowledge in the area may still be viewed as “certain enough.”