: External - Tolkien wrote the rhyme some time before his ideas
: on the origin of the rings had crystallised, and the
: inconsistancy is a result of this.

He went through a number of variations on the rhyme, but I'm not sure at what point the final theme crystalized. That would take, I think, a considerable amount of research.

: Internal - Though the elven smiths thought they were making
: them for their own use and purposes, Sauron had warped them
: during their construction, or design, towards his own purposes;
: which included a pre-determined adaption of the Nine to human
: use, and the Seven to Dwarven use.

Some people have argued this, but the textual evidence is contrary to this point of view. Sauron's intention was to ensnare the Elves. The plan to use the Rings on Men and Dwarves was not devised until after he captured the Seven and the Nine.

: Here's a possibly interesting question - If the rings had no
: pre-adaptation why did Sauron not use some or all the Seven,
: when they came into his possession, to enslave more human
: Nazgul? Tolkien says that the rings did not have the same
: effect on Dwarves as on men, but if the rings were all of a
: similar nature surely Sauron would have used them to create
: sixteen such useful human servants as the Ringwraiths.

But why leave out the Dwarves? One must wonder if he would regret giving the Rings to Dwarves after he realized they wouldn't give him the mastery over Dwarves he desired.

------------------
Talk About J.R.R. Tolkien and Middle-earth: A Guide To Tolkien Discussion on the Web