William
OK so "nonsense" equals not potentially knowable. And OK with your example in the sense that this incident, ie of a bus passing, will not occur (assuming this is mot a bus route and a bus just doesn't happen to use that roads!). The real point is it did not occur, so it is not potentially knowable.
"So what is the line between and all of the possibilities which don't exist "
Answer: whether it potentially could manifest to us. Something does not exist, for us, if it did not occur, or possibly occurred but not within the form of existence knowable to us. Because, for a scientific explanation of our physical existence, we cannot just 'make it up'. There has to be a basis built on, and a derivation confined by, what has proven experienceability. There are countless occurrences happening billions of miles away which we do not know, but they are potentially knowable. Nearer earth, there is an anomaly in an orbit which demonstrates that something else is there which we cannot detect directly.
"I take the stance of saying everything is knowable to us, and that which is unknowable eventually gets drawn into the knowable as we develop as thinkers and human beings"
No. Everything which is potentially knowable, is potentially knowable (apologies for the grammar). It is then a matter of whether we will get to know that or not. Although it appears superficially intellectual to start with no presumptions, this is not only not possible, it is wrong. Because we are part of existence, so there is an inherent presumption, and, putting that a different way, physical existence is not an abstract concept, it occurs in a definitive form. So, the danger in ignoring that and thinking 'all options are possible' is that one is selected which does not correspond with reality, as it is to us. Of course, having selected that then a theory based thereon can become self-fulfilling. If at any time there appears to be a contradiction, because actually it does not correspond with reality, one just invokes some corrective mechanism. The underlying problem being that since it has no real basis, then it is difficult to falsify.
Paul