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3.2. nasale vowels
We distinguish between nasale and orale vowels. In English we have only orale vowels. That means that you can pronounce any English vowel holding your nose closed. It doesn't make any difference, just try. That has the big advantage that your pronunciation doesn't change if you got a cold.
(The case of nasale sounds is completely different. M and n for instance are pure nasale sounds, only the nose serves as a resonance body. If you press your noise the air stream can be parked for a second in the mouth, if there is no space left in your mouth, your m and n stopps. Just try.)
In French and Portuguese there are nasale vowels as well. Very probably the nasale vowels are a heritage of the celtic, they gave this way an individual note to latin. In the case of nasales vowels the nose is used as a resonance body.
A nasale vowel can be distinguished very easily from an oral vowel if we hear it and therefore we will hear several hundreds of example in this introductory chapter about the pronunciation and several thousands in the whole book, but it is difficult to explain what it is. The first thing we have to understand is that the mouth and the nose are connected and this connection can be opened or closed by the uvula. (That is this little peace above at the end of the oral cavity you see if you look with the open mouth into the mirror and that hurts sometimes if you get a cold. If you don't see that this connection can't be closed, pronounce a t or a d. In the case of a t or a d you have to stow the air behind your tongue and let it out suddenly. In order to do that, you have to close the connection between the nose and the moth, otherwise it wouldn't be possible to stow air your moth, because the air would flow out through the mouth. Therefore it is cliear that you can interrupt the connection by lifting the uvula. This is done inconsciously therefore perhaps you have never noticed it, but it is possible, otherwise you wouldn't be able to speak.
If we want to understand what is a nasale vowel we can pronounce a aaaaaaaaaaaa. First with closing the nose, so that we can be sure that it is a oral vowel. Than we open the nose and move the dorsum or back of the tongue slowly backwards. We will get to a point where part of the air stream can't flow out through the mouse any more and has to flow out, provided that the uvula is not liftet, through the nose. That sounds different. If it is still unclear what a nasales vowel is, it will become clear in the next chapters, wenn we illustrate it with voice examples, but you get a general idea.
The same thing can be done with ooooooo, iiiiiiiii, uuuuuuuuuuu and eeeeeee. To any oral vowels exists a nasale version. However with the nose only we couldn't form different nasale vowels, because unless you have a very special nose, in other words unless you can influence the form of your nose by special muscles, the resonance body of the nose is always the same. With the nose alone you can only produce one sound. Nasale vowels are formed therefore by using the nose and the mouth as a resonance body.
If you have studied French at school you may have wondered why they are written en / em, an / am, in / im, on / om, un. This is due to the fact that in the course of history, very probably under the influence of celtic, an oral vowel became pronounced as a nasal vowel if he stays in front of a nasal consonant and m and n are nasal consonants. It works the same way in Portuguese. Any combination of vowel + m is pronounced nasale.
Portuguese pronunciation, concerning this point it is similar to French, is complicated. That's why the chapter about pronunciation is the largest one of the whole book with hundreds of examples and a detailed description how they should be pronounced.