The way the sentence is written, it almost makes it look as though glottalization is what distinguishes between non-sonorants and sonorants - but to state the obvious, it's simply the [+/-sonorant] feature that differentiates them. Glottalization affects only sonorants, as I'll explain below.

I apologise if I'm repeating something you already know here, but this is a crucial point: "opposition" refers to a contrast between a pair of segments which differ in a single feature. [p] and [b] are opposed in that [p] is voiceless but [b] is voiced - so in this pair of segments, voicing is said to be "contrastive" (it sets the two segments apart).

What your sentence means is that glottalization is contrastive in (pairs of) consonants - though NB only in (pairs of) sonorant consonants. We are told that non-sonorants are always simple (Gussenhoven & Jacobs use "simple" vs. "complex", "plain" I haven't come across). This means that they are *phonetically* simple, i.e. they have only a single articulation. Glottalized segments, however, are complex since by glottalizing a segment you're adding a secondary articulation - so non-sonorants can never be glottalized in this language.

Sonorants, meanwhile, are divided into pairs (see the table I refer to below) where you have one segment which lacks glottalization (e.g. m or n in the table) and another which does have it (it's marked with what looks like a superscript question mark minus the dot at the bottom, which is added to m/n etc.) - otherwise, they are identical in terms of features.

There's a good explanation here, which may clarify things (note the table on page 16, where non-sonorants are never glottalized but sonorants can be simple *or* glottalized):

"O sistema Dâw opõe pelo traço de glotalização as duas classes maiores de consoantes: sonorantes e não-sonorantes. **As consoantes sonorantes podem ser glotalizadas, isto é, podem ter uma articulação glotálica adicional e elas são nasais, laterais e aproximantes**

(To recap: sonorants can be glottalized, i.e. can bear an additional glottalic articulation).

As **não-sonorantes** são compostas pelas oclusivas e fricativas e **são sempre plenas. As consoantes plenas são definidas como aquelas que possuem somente uma articulação**."

(Non-sonorants are always simple, and simple consonants are ones which possess only a single articulation).
http://www.lotpublications.nl/publish/articles/001020/bookpa...

"Sendo que" seems to mean something more like "since" or "in that" here, if anything - certainly not "even though", since the part of the sentence after that explains/clarifies what comes before it.







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Note added at 3 days6 hrs (2007-09-02 02:31:46 GMT)
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To fit this into the sentence, which I forgot to add - you could put something like "and glottalization is contrastive since although non-sonorants are always simple..."

Note also that there's an important difference between glottal and glottalized consonants - in glottal segments, such as [h], "glottal" is the primary (and only) place of articulation. In glottalized segments - such as the m with a superscript question mark minus a dot in the table I quoted above - glottalization is merely a secondary articulation, while the primary place of articulation is still labial as it would be for a normal [m].

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Note added at 6 days (2007-09-05 09:26:37 GMT)
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See also

Just as for vowels, one language may make use of a consonant dimension which other languages do not. Two of the languages on our list, Amharic and Tzeltal, have an alternate way of producing stops and affricates. This mode of production involves a buildup of pressure behind the point of contact and an explosive release accompanied by a glottal stop; such consonants are referred to as ejective consonants. I will use a following apostrophe to indicate these sounds and will refer to this dimension as **glottalization**... there are glottalized stops, fricatives, affricates, and sonorants in different languages.

Glottalization is used **contrastively** in Amharic and Tzeltal. That is, the sounds /t'/, /č'/, and /k'/ are used, like /t/, /č/, and /k/, to make distinct words in these languages... To show that **glottalization is contrastive** in Amharic, we can cite pairs like /kok/ 'peach' vs. /k'ok'/ 'partridge' and /tɪl/ 'worm' vs. /t'ɪl/ 'quarrel'.
http://www.indiana.edu/~hlw/PhonUnits/consonants2.html