<productname>PostgreSQL</productname> provides the
standard <acronym>SQL</acronym> type <type>boolean</type>;
see <xref linkend="datatype-boolean-table">.
- The <type>boolean</type> type can have one of only two states:
- <quote>true</quote> or <quote>false</quote>. A third state,
- <quote>unknown</quote>, is represented by the
+ The <type>boolean</type> type can have several states:
+ <quote>true</quote>, <quote>false</quote>, and a third state,
+ <quote>unknown</quote>, which is represented by the
<acronym>SQL</acronym> null value.
</para>