[Boromir88]

Before I can maybe shed some light on 'sorcery' in Tolkien, I think it will be good to give a little background of magic in general.

I think magic comes in two basic forms in Tolkien's story...the Art Form and the Sorcery Form.

The Art form is the creative side of magic...healing, entertainment, protecting. This is the form that Elves seems to be most comfortable with. It tends to be the better side of magic. Some examples...Gandalf's Fireworks, Elrond or Aragorn's healing abilities, Galadriel's mirror.

Then there is the Sorcery form, which is the offensive or destructive magic. Sorcery is much easier to be used for evil purposes, although I don't think Sorcery is always, all the time, 'evil.' It's just that Sorcery is much easier to use for the purposes of Evil, than the art side of magic.

I do not intend to involve myself in any debate whether ’magic’ in any sense is real or really possible in the world. But I suppose that, for the purposes of the tale, some would say that there is a latent distinction such as once was called the distinction between magia and goeteia. Galadriel speaks of the ’deceits of the Enemy’. Well enough, but magia could be, was, held good (per se), and goeteia bad. Neither is, in this tale, good or bad (per se), but only by motive or purpose or use. Both sides use both, but with different motives. The supremely bad motive is (for this tale, since it is specially about it) domination of other ’free’ wills. The Enemy’s operations are by no means all goetic deceits, but ’magic’ that produces real effects in the physical world. But his magia he uses to bulldoze both people and things, and his goeteia to terrify and subjugate. Their magia the Elves and Gandalf use (sparingly): a magia, producing real results (like fire in a wet faggot) for specific beneficent purposes. Their goetic effects are entirely artistic and not intended to deceive: they never deceive Elves (but may deceive or bewilder unaware Men) since the difference is to them as clear as the difference to us between fiction, painting, and sculpture, and ’life’~Letter 155

Here, Tolkien talks about magia and goeteia.

goeteia, sounds more to be the psychological mind games. The Enemy uses goeteia to dominate over other wills, install fear and sub-ordination. Where the Elves and those like use goeteia entirely for artistic purposes. (Galadriel perhaps as an example?)

Then comes magia, which is actual physical effects in the world...Tolkien notes the fire in the wet faggot. Again, here magia isn't bad by nature, but can be used for evil purposes...all depending upon the motives one uses it. Is it for beneficial reasons, as Gandalf uses? Or is it to destroy and bulldoze?

The best example of Sorcery I can give is Saruman's 'Fire of Orthanc.' A lot of people tend to think that the explosions Saruman employs at Helm's Deep was just first invention of gunpowder. I however, think it's clear Saruman uses his skill in sorcery to create the explosives. Letter 155 goes on to say:

The basic motive for magia - quite apart from any philosophic consideration of how it would work - is immediacy: speed, reduction of labour, and reduction also to a minimum (or vanishing point) of the gap in time between the idea or desire and the result or effect.

A use for magia is to reduce labor and increase speed. If we look at this quote, I think it fits perfectly with the 'Fires of Orthanc,' used at Helm's Deep. Saruman needed to breach the defenses as quick and easy as possible. So, it's entirely plausible that Saruman uses his magia here (the Sorcery form), to create the 'fires of Orthanc' and break a gaping hole in the Helm's Deep defenses. As, this would greatly reduce the amount of labor and time it took to breach the defenses.

However, I don't think that Sorcery is evil at all, just the motives one uses it are, and since it is more of the offensive form of magic, it is more easily used with evil motives than the artistic form. Elves were most comfortable with with the Art form, though Sorcery could be useful to them as well...as an example Finrod's confrontation with Sauron on the isle of Tol Sirion.

Great spells were matered by the Lord of the Nazgul & the Mouth of Sauron, yet they must have had a source.

I don't know about Men being able to 'Master' Sorcery, however it is clear that Men were able to learn it. You bring up the Witch-King and the Mouth of Sauron. Men naturally are less capable of magic because they aren't born with that ability it seems, they have to learn it from another source as you mentioned.

The Nazgul got theirs from their rings:

Those who used the Nine Rings became mighty in their day, kings, sorcerers, and warriors of old~The Silmarillion; Of the Rings of Power and the Third Age

And the Mouth of Sauron was rumoured to have learned Sorcery from Sauron:

...and because of his cunning he grew even higher in the Lords' favour...and he learned great sorcery, and knew much of the mind of Sauron.~The Black Gate Opens

I would also like to point out the Blade of the Westernesse was a blade wrought with spells for the bane of Mordor (The Witch-King). So, where did the Witch-King's enemies, come up with the ability to create swords that were designed to destroy the Witch-king...and I think it's easily established that the special sword did it's purpose:

No other blade, not though mightier hands had wielded it, would have dealt that foe a wound so bitter, cleaving the undead flesh, breaking the spell that knit his unseen sinews to his will.~Pelennor Fields

I think the 'magic beings'...like Sauron, Gandalf, the Elves...etc had the inherent power, and capability to use magia for the Art Form or the Sorcery form. Where Men were non-magical beings and it had to be learnt by them. It could be learnt by Men, but at what price for them, becomes a good question?

Edit: As I was posting along with lmp...this is just something I have thought about. Perhaps we have magia (the physical, actual effects in the world) the goeteia (the mental effects) and both can be broken down into the Artistic form of magic and the Sorcery form of magic?