I have been doing OT through lock-down basing my studies on this book, A course in Phonology - 1999.
I have the following problem: in p. 510 (markedness statements/ constraints) we find that :
19 r. is given as one of the prohibitions that is "assumed to be inviolable, as a matter of sheer physics"
*[+ nasal, - sonorant] (says that this can be expressed as (=nasals cannot be obstruent)
[m] and [n] are nasals and obstruent (in the vocal tract)
Obstruent is defined as: obstruction in the oral cavity, which includes labial as per tree in p. 530. [b] and [m] are consonants (to use the old parlance) and bilabial.
So how can 19 r be "inviolable" when child speech uses b and m as perhaps their first consonsants. They are the "easiest" consonants to pronounce.
I agree that in vowels (sorry the term sonorant takes getting used to, as per chart - Halle's - at the end of the book) they of course have to be voiced/sonorants (and can be nasalised).
But nasals cannot be obstruent ? Perhaps cannot be non sonorants. If not (by vocal tract obstruction) they would not be articulated.
So we are left with /a,i,u/ and consonant /t/ (p. 586) as the segmental inventory of natural languages. Is this science ?