Suppose in a certain place there's a 30% chance of rain ... and suppose there's an east wind blowing, so there's a 15% chance of rain ... which is it? 15%? 30%? depends on what we agree we know about the situation - it is something of a 'crypto-signature' on an agreed route.
To the chemist, probability, connotes, mensurability, the temporal ability to definitively measure a quantity - a bottom line to numeric precision, within which the chemical experiment will yield the same result repeatedly [within a feasible possibility of utility] ... but once the experiment becomes commercial, the margin must be enlarged to minimize or [in the case of military TEMPEST single-point-failure rules] make never within the usetime of the process sold.
The word itself, probability, connotes probe-ability, the ability to probe, meaning, penetrate, sample, test, prove ... something, or by some means. Thus it can't be 50% probe-able unless a portion remains un-known-able: probe-ability itself must be a measure of the information dis-cover-able with respect to the information content [available to/by better probe-ability].
[under construction, and arithmetic needs re-checking]
A premise discovery under the title,