Oldak Quill wrote:
Let me give you an example. If I were writing an article on a drug and I included the sentence "tyrosine is an amino acid", I would be expressing a relation that is learnt in secondary education. It being an amino acid is the first thing anyone would learn about tyrosine. Is this reference worthy?
Yes. Either you have a one-sentence stub article, in which case its one required reference could be almost any textbook or webpage mentioning tyrosine, or else you have additional material in the article, whose required source will also happen to mention tyrosine's amino-acid-ness.
Incidentally, one of the interesting side-effects of looking up references is that one regularly discovers that the "common knowledge" from secondary education days is now many years out of date, and no longer correct.
Stan