diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst
--- a/Doc/library/argparse.rst
+++ b/Doc/library/argparse.rst
@@ -607,8 +607,8 @@
 -------------------------
 
 .. method:: ArgumentParser.add_argument(name or flags..., [action], [nargs], \
-                           [const], [default], [type], [choices], [required], \
-                           [help], [metavar], [dest])
+                           const=None, default=None, [type], [choices], \
+                           [required], [help], [metavar], [dest])
 
    Define how a single command-line argument should be parsed.  Each parameter
    has its own more detailed description below, but in short they are:
@@ -909,21 +909,25 @@
 default
 ^^^^^^^
 
-All optional arguments and some positional arguments may be omitted at the
-command line.  The ``default`` keyword argument of
-:meth:`~ArgumentParser.add_argument`, whose value defaults to ``None``,
-specifies what value should be used if the command-line argument is not present.
-For optional arguments, the ``default`` value is used when the option string
-was not present at the command line::
+The *default* keyword argument of :meth:`~ArgumentParser.add_argument`
+(default: ``None``) specifies what value to use if a non-required argument
+is omitted from the command line.  For optional arguments, this occurs when
+the option string is not present (but not when the option string is present
+with no arguments --- see const_ for that case)::
 
    >>> parser = argparse.ArgumentParser()
    >>> parser.add_argument('--foo', default=42)
-   >>> parser.parse_args('--foo 2'.split())
+   >>> parser.parse_args(['--foo', '2'])
    Namespace(foo='2')
-   >>> parser.parse_args(''.split())
+   >>> parser.parse_args([])
    Namespace(foo=42)
 
-If the ``default`` value is a string, the parser parses the value as if it
+For positional arguments, an argument can be omitted when nargs_ equals
+``'?'`` or ``'*'``.  If *nargs* equals ``'*'`` and *default* is ``None`` for
+a positional argument, an empty list ``[]`` is used as the default value
+instead of ``None``.
+
+If *default* is a string, the parser parses the value as if it
 were a command-line argument.  In particular, the parser applies any type_
 conversion argument, if provided, before setting the attribute on the
 :class:`Namespace` return value.  Otherwise, the parser uses the value as is::
@@ -931,22 +935,11 @@
    >>> parser = argparse.ArgumentParser()
    >>> parser.add_argument('--length', default='10', type=int)
    >>> parser.add_argument('--width', default=10.5, type=int)
-   >>> parser.parse_args()
+   >>> parser.parse_args([])
    Namespace(length=10, width=10.5)
 
-For positional arguments with nargs_ equal to ``?`` or ``*``, the ``default`` value
-is used when no command-line argument was present::
-
-   >>> parser = argparse.ArgumentParser()
-   >>> parser.add_argument('foo', nargs='?', default=42)
-   >>> parser.parse_args('a'.split())
-   Namespace(foo='a')
-   >>> parser.parse_args(''.split())
-   Namespace(foo=42)
-
-
 Providing ``default=argparse.SUPPRESS`` causes no attribute to be added if the
-command-line argument was not present.::
+command-line argument was not present::
 
    >>> parser = argparse.ArgumentParser()
    >>> parser.add_argument('--foo', default=argparse.SUPPRESS)