Four or more formal classes of nouns, genders, are distinguished. According to Corbett (2008), Dyirbal, Tsez, and Pirahã are examples of such languages. 

<br><br><b>Reference</b><br>
Corbett, Greville G. 2008. Number of Genders.
In Haspelmath et al. (2008), chapter 30.
Available online at <a href="http://wals.info/feature/30"> http://wals.info/feature/30</a href>. 
