J.R.R. Tolkien said:
[Eru/God] gave special 'sub-creative' powers to certain of His highest created beings: that is a guarantee that what they devised and made should be given the reality of Creation. Of course within limits, and of course subject to certain commands or prohibitions. But if they 'fell', as the Diabolus Morgoth did, and started making things 'for himself, to be their Lord', these would then 'be', even if Morgoth broke the supreme ban against making other 'rational' creatures like Elves or Men. They would at least 'be' real physical realities in the physical world, however evil they might prove, even 'mocking' the Children of God. They would be Morgoth's greatest Sins, abuses of his highest privilege, and would be creatures begotten of Sin, and naturally bad. (I nearly wrote 'irredeemably bad'; but that would be going too far. Because by accepting or tolerating their making necessary to their actual existence even Orcs would become part of the World, which is God's and ultimately good.) But whether they could have 'souls' or 'spirits' seems a different question; and since in my myth at any rate I do not conceive of the making of souls or spirits, things of an equal order if not an equal power to the Valar, as a possible 'delegation', I have represented at least the Orcs as pre-existing real beings on whom the Dark Lord has exerted the fullness of his power in remodelling and corrupting them, not making them.