Reword

Author: StanFromIreland

Doc/faq/design.rst

@@ -422,8 +422,10 @@ two to the directory.
 
 Tuples are immutable, meaning that once a tuple has been created, you can't
 replace any of its elements with a new value.  Lists are mutable, meaning that
-you can always change a list's elements.  Only immutable elements can be used as
-dictionary keys, and hence only tuples and not lists can be used as keys.
+you can always change a list's elements.  Only hashable objects can be used as
+dictionary keys. Most immutable types are hashable, which is why tuples, but
+not lists, can be used as keys. Note, however, that a tuple is only hashable
+if all of its elements are hashable.
 
 
 How are lists implemented in CPython?