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[PhilOfPerth]

Looking at the original post, I'd have to say:

1) I'm with Rho.  Just use _True and _False.  They're built in the language now.

2) If one has to define a value themselves, then I prefer either of the first two methods.  In basic True is always NOT FALSE, but FALSE isn't always NOT TRUE.

FALSE is *only* NOT TRUE when True is -1, but BASIC considers any non-zero value to be True.

2 is True.  NOT 2 is.. -3.  Which is also True.

0 is False.  That's the only guarantee BASIC makes.  Saying True = NOT FALSE will always be correct.  Thinking FALSE = NOT TRUE is only correct in the limited scope of *IF TRUE = -1*.  When dealing with CONST, there's nothing wrong with writing it as your third example does, with the exception that it reinforces the concept that False = Not True, which isn't a true statement all the time.

If one is going that route, then they could probably just use FALSE = _NEGATE True.  Then that statement would always be valid and correct.

2 = True.  _NEGATE 2 = 0.  Which is, indeed, False.

A subtle difference, but one that I think if someone learned to adapt to, it might save them some issues later down the road.  NOT TRUE can still sometimes be TRUE, but _NEGATE TRUE will always be FALSE.

Pardon? 
As someone famouser than me once said, "what is truth?" (no, I don't think it was Trump).