Comment by weinzierl

The official rule I learnt in my English (as foreign language) classes is vowel = thee and consonant = thuh. That's it.

But I noticed that native speakers deviate from this at least in two cases:

1. Use thee to emphasize the following noun

2. When searching for the noun to say, they often get it wrong because they say something like "uh, thee, thee, thee, uh, book" and never sweat it.

Source: I watched a lot of Monty Python as a kid and John Cleese does this all the time.