The Arbitrary ChuckJerry

Here's a random thought. I have been using the idiom "all of a sudden" for as long as i can remember. Recently I've heard people say "all of THE sudden" instead of the "A sudden", which is how I thought it was. Obviously this is a dissonance that I cannot tolerate, so I did some research.

Aparently I am right. The proper usage is "all of a sudden", though there doesn't seem to be any particular grammatical reason for it, just that that's how the idiom goes.

So this time I was right, but I have been wrong in the past about idioms. For the longest time I thought that something was done "for all intensive purposes", and even used the term in a college philosophy paper. Only at that point when the phrase was met with a resounding x mark in red pen was I made aware that something is done "for all intents and purposes" instead.