By adding the word “True” in the definition, any examples brought forth to refute the definition are discounted because they are examples of the true definition. This means the definition cannot be tested and negates the ability to discuss.
The title comes from the classic example of “All Scotsmen are brave”, ‘X is a Scotsman and isn’t brave’, “Then X is not a True Scotsman”. Even if X was born and bread from a long traditional Scottish line, X is now defined as not a True Scotsman because they don’t fit the definition. Another common example is “Schizophrenia is a chronic disease”, ‘Y was diagnosed with schizophrenia but then got over it’, “then Y either went into remission or never had schizophrenia to begin with”. The counter example is discounted because it doesn’t fit the definition of “chronic” (pervasive and life long).
If I define gravity as an attractive force between any two masses, then that is what it is. The falsifiable test for this idea is to try to locate a mass that does not respond with attraction to another mass. If I find matter that does this, then clearly my definition of gravity is in error and needs to be modified, or the definition of “mass” is in error and needs to be modified. One does not simply exclude the counter example because it isn’t “True Gravity”.
In other words, if all counter examples are excluded, then the definition has no real meaning. “All True Beds have a monster under them”, ‘I found no monster under my bed’, “Well then, it isn’t a True Bed, then is it?” This assertion can never be disproved, while the assertion that all beds have monsters under them can be. By framing it in the True Scotsman variant, the burden of proving the statement is removed as the evidence is discounted.