My French teacher said that you would pronounce the "h" in words like haut and hall, that have an h aspiré. However, my previous French teacher said that the "h" aspiration does not exist at all in French. Which one is correct?
In French, "h" is never pronounced like English /h/. It's always inaudible... but it can have an effect!
The « h aspiré » is a phenomenon where a word starts with a zero phoneme. Basically, you have to pretend it starts with a consonant even though you don't hear anything.
Why is that important? Because consonants affect how words run together.
For example, words that start with consonants don't allow elision. Neither does a word that starts with an « h aspiré » :
l'orange mais le pays (orange starts with a vowel but pays starts with a consonant)
l'homme mais le héros (homme has an « h muet » but héros has an « h aspiré »)
Words that start with consonants also don't allow liaison. Neither does a word that starts with an « h aspiré » :
cet orange mais ce pays
cet homme mais ce héros
There are other similar alternations, but hopefully these examples make the pattern clear.
How do you tell whether a word has an « h aspiré » or an « h muet » ?
The Wikipedia article lists some ideas, though nothing is failsafe and most are hard to do on the fly. For example, it says that Germanic words tend to have an « h aspiré » while Latinate words have an « h muet ». But how do you know which words are Germanic if you're not a linguist?
The failsafe way is to check a dictionary (as usual), where it will be marked in the pronunciation.
For example, here's the WordReference pronunciation for homme with its « h muet ». Notice how the first symbol is a vowel:
But here's the pronunciation for « héros » with its « h aspiré ». Notice that the first symbol is an apostrophe:
I'll want to add that it also affects liaison. "un homme" is pronounced /ɛ̃ nɔm/ while "un héros" is pronounced "ɛ̃ 'eʀo/. Oct 20, 2017 at 0:46
In addition to Luke answer which clearly explains the h aspiré issue, note that despite the fact the letter "h" is never pronounced and thus that there is no [h] consonant listed in the phonetic French alphabet, the sound [h] can nevertheless be heard in spoken French without relationship between the presence or not of the letter "h", especially at the beginning of sentences with a stressed first vowel.
For example, the sentence:
Et alors ?
is sometimes pronounced with a leading [h], \ he alɔʁ \ instead of \ e alɔʁ \
We make no distinction between the variants.
That also explain why the French accent often mix up words like "and " and "hand", "to heat" and "to eat"...