In the book Fuzzy Logic with Engineering Applications by Timothy J. Ross, it is written we can't write "De Morgan's laws"; instead, it should be "De Morgan's Principles". The authors used only "De Morgan's Principles" throughout the book.
I want to ask:
Is there any difference between the two phrases, or are they the same?
Thank you!
These are lines from the same book (3rd ed.) ref. by @ Mauro ALLEGRANZA. I hope these lines clear the point if someone else has the same confusion:
"The operations due to De Morgan are also not be referred to as a law, but as a principle . . . since this principle does apply to some (not all) uncertainty theories (e.g., probability and fuzzy). The excluded middle axiom (and its dual, the axiom of contradiction) are not laws; Newton produced laws, Kepler produced laws, Darcy, Boyle, Ohm, Kirchhoff, Bernoulli, and many others too numerous to list here all developed laws. Laws are mathematical expressions describing the immutable realizations of nature. Definitions, theorems, and axioms collectively can describe a certain axiomatic foundation describing a particular kind of theory, and nothing more; in this case, the excluded middle and other axioms can be used to describe a probability theory. Hence, if a fuzzy set theory does not happen to be constrained by an excluded middle axiom, it is not a violation of some immutable law of nature like Newton’s laws; fuzzy set theory simply does not happen to have an axiom of the excluded middle – it does not need, nor is constrained by, such an axiom." from (Fuzzy Logic with Engineering Applications by Timothy J. Ross)