I tried following the example from here (http://catcode.com/teachmod/chmod_cmd2.html):

Open up publicity.html for reading and writing by anyone.

Before:  -rw-r--r--  publicity.html
Command: chmod og=rw publicity.html
After:  -rw-rw-rw-  publicity.html

Here's my terminal session:

username@ubuntu:/etc$ -rw-r--r-- bash.bashrc
-rw-r--r--: command not found
username@ubuntu:/etc$ chmod og=rw bash.bashrc
chmod: changing permissions of `bash.bashrc': Operation not permitted
username@ubuntu:/etc$ -rw-rw-rw- bash.bashrc
-rw-rw-rw-: command not found