diff --git a/calendar/teachingdates/config/cli.py b/calendar/teachingdates/config/cli.py
index 81e5776..5fc7b8d 100644
--- a/calendar/teachingdates/config/cli.py
+++ b/calendar/teachingdates/config/cli.py
@@ -4,6 +4,30 @@
 from teachingdates import PROG
 
 
+def oxford_comma_list(words):
+    if isinstance(words, list) or isinstance(words, tuple):
+        if len(words) == 0:
+            return ""
+        elif len(words) == 1:
+            return words[0]
+        elif len(words) == 2:
+            return " and ".join(words)
+        else:
+            return ", ".join(words[:-1]) + ", and " + words[-1]
+    else:
+        raise TypeError("expected list, got {t}".format(t=str(type(words))))
+
+
+def switch_message(switches, context, severity="warning", required=False):
+    switch_string = oxford_comma_list(switches)
+    return ("{prog}: {severity}: {switches} {verb} {required} for "
+            "{context}".format(prog=PROG,
+                               severity=severity,
+                               switches=switch_string,
+                               verb="are" if len(switches) > 1 else "is",
+                               required="required" if required else "ignored"))
+
+
 def parse_command_line():
     """Parse command-line arguments.