I have found that, in speaking, there are subtle differences in the way words are pronounced based upon the context.
For me it is "only natural" to change "THE" from a short sound to a long sound when preceeding a word that begins with a vowel.
I say, (phonetically) "`Thee` educated man" but "`Thu` mild-mannered man".

Is there a word for this? Is it common or simply my 1950's Philadelphia* upbringing?

*"Did you ever notice how many people are FROM Philadelphia?" - W.C. Fields

"I am certain there is too much certainty in the world" -Michael Crichton