John,
J. M.,
not
J. M.
John.
This plainly contradicts the principle “nothing before something.” A period is too trifling a matter to arrange by, and neglecting that
| J followed by nothing | J | |
| should precede | J followed by o, | John. |
The third exception is this:
A book written by a single author should precede one written by him and another.
(See the argument in the note to § [240].)