In varieties of African-American English, the interdental fricatives are realized as either alveolar stops or labiodental fricatives, depending upon the location of the fricative in the word.
When located at the beginning of a word, the interdental fricative 
is realized as 
. For example, the word thin 
is pronounced as 
. When located word-medially or word-finally, the interdental fricative is realized as 
. For example, the word bath 
is pronounced as 
.
When located at the beginning of a word, the interdental fricative 
is realized as 
. For example, the word this 
is pronounced as 
. When located word-medially or word-finally, the interdental fricative is realized as 
. For example, the word brother 
is pronounced as 
.
It is important to note that these rules are quite consistent. In African-American English, it is ungrammatical to pronounce as unless it is at the beginning of a word (bath *
), and it is ungrammatical to pronounce as if it is at the beginning of a word (thin *
). The same holds true of the voiced interdental fricative.
Smitherman (X) notes the lack of interdental fricatives in West African languages to account for this rule in African-American English, using this as support for a West African source for some features of African-American English.