In Odd Language #115: When Rules Collide, I wrote about a simple case of ordinary English rules causing trouble when applied to E-mail addresses. A simple hyphenation rule ends up creating an erroneous E-mail address.
Were that the only area where rules collide!
The world has many cases of a rule that makes sense within its own area causing trouble when it collide with a rule from another area.
I had an example of this nearly happening to me when I was getting set to attend university.
The dorm rules included that one had to pay one’s rent for the semester so many days before the start of the semester. This made sense, because they need to be able to get answers to people as to whether they have room for them for the semester.
My funding had a rule that they would not pay out any amounts until so many days before the start of the term. The made sense, because of people abusing the system in the past by getting lump sums and then never attending.
Unfortunately, the funding time was less than the dorm time. Fortunately, the dorm administration was flexible enough that if you had firm proof of your funding, they would accept that.
What if they did not, and someone had no other way to pay?
Something making sense in its own area is not enough for it to make sense in general.