I always thought that both noon and midnight are *neither* am nor pm, and I contend that correct usage demands employment of the word "noon" or "midnight," without any suffix, instead of the number "12" (with either suffix).

I would contend that "12 am" and "12 pm" constitute incorrect use of language, and have observed that those who use these constructions do not use them consistently (i.e, "12 am" could mean *either* noon or midnight, depending upon the source).

Insofar as the "m" in "am/pm" stands for "meridian," meaning "noon," noon itself cannot be 12 hours before itself (ante meridian) or after itself (post meridian). Midnight, on the other hand, is *both* 12 hours before *and* 12 hours after noon.