Are 勅 and 詔 simply synonyms?


I cannot find a clear difference between these two kanji:

> 勅 : Imperial decree (みことのり、ショウ)
>
> 詔 : Imperial edict (みことのり、チョク)

The English definitions for "decree" and "edict" are so similar, I think the
only main difference I could pinpoint was that "decree" had the aspect of
formality (although it seems to me that an edict is also formal)

> edict: noun 1) a decree issued by a sovereign or other authority. 2) any
> authoritative proclamation or command.
>
> decree: noun 1) a formal and authoritative order, especially one having the
> force of law.

(You will notice "decree" is used to define "edict"...)

The Japanese definitions of these kanji are also similar, but I'm not adept
enough to read into the subtleties:

> 勅: １ 天子の命令。天皇の言葉。また、それを記した文書。みことのり。 ２ 尊貴の者からの命令。
>
> 詔: 天子の命令を直接伝える文書。みことのり。詔書。

The second definition for `勅` says it could be used to mean orders from people
beneath the level of the Emperor.

So my question are these kanji just interchangeable synonyms that mean
`天子の命令`, or is there a definite difference (other than the secondary
definition)? Normally I would write them off as synonyms, but I feel that
there are often specific words for things when dealing with traditional
Japanese customs, etc.




Fefe pointed me towards a link in the comments, so I read up on it. [(see
here)](http://ja.wikipedia.org/wiki/%E8%A9%94%E5%8B%85#.E5.85.AC.E6.96.87.E5.BC.8F.E4.BB.A5.E5.89.8D)
It seems that these two kanji are used together (`詔{しょう}勅{ちょく}`) to mean an
“an Imperial decree or edict”.

However, they have separate meanings as well, which are `詔{しょう}書{しょ}` and
`勅{ちょく}書{しょ}`. From what I can tell, the main difference seems to be:

  * `詔書` would require the Imperial court to sign off on it. Apparently getting a `詔書` signed was a pain, so it ended up being used for very official, formal things, like a `改{かい}元{げん}` (changing of an era).
  * `勅書` did not require full ratification and was used for more urgent or day-to-day matters.




Fefe pointed me towards a link in the comments, so I read up on it. [(see
here)](http://ja.wikipedia.org/wiki/%E8%A9%94%E5%8B%85#.E5.85.AC.E6.96.87.E5.BC.8F.E4.BB.A5.E5.89.8D)
It seems that these two kanji are used together (`詔{しょう}勅{ちょく}`) to mean an
“an Imperial decree or edict”.

However, they have separate meanings as well, which are `詔{しょう}書{しょ}` and
`勅{ちょく}書{しょ}`. From what I can tell, the main difference seems to be:

  * `詔書` would require the Imperial court to sign off on it. Apparently getting a `詔書` signed was a pain, so it ended up being used for very official, formal things, like a `改{かい}元{げん}` (changing of an era).
  * `勅書` did not require full ratification and was used for more urgent or day-to-day matters.

