What does "they" refer to here?

Context:

Free will is the ability of http://en.wikipedia.org/wiki/Agency_(philosophy) to make http://en.wikipedia.org/wiki/Choice unconstrained by certain factors. Factors of historical concern have included metaphysical constraints (such as logical, nomological, or theological http://en.wikipedia.org/wiki/Determinism), physical constraints (such as chains or imprisonment), social constraints (such as threat of punishment or censure, or structural constraints), and mental constraints (such as compulsions or phobias, neurological disorders, or genetic predispositions). The principle of free will has http://en.wikipedia.org/wiki/Religion, http://en.wikipedia.org/wiki/Law, http://en.wikipedia.org/wiki/Ethics, and http://en.wikipedia.org/wiki/Science implications.^[1] For example, in the religious realm, free will implies that individual http://en.wikipedia.org/wiki/Will_(philosophy) and http://en.wikipedia.org/wiki/Choice can coexist with an http://en.wikipedia.org/wiki/Omnipotent http://en.wikipedia.org/wiki/Divinity. In the law, it affects considerations of http://en.wikipedia.org/wiki/Penology and http://en.wikipedia.org/wiki/Rehabilitation_(penology). In ethics, it may hold implications for whether individuals can be held http://en.wikipedia.org/wiki/Moral_responsibility for their actions. In science, http://en.wikipedia.org/wiki/Neuroscience_of_free_will may suggest different ways of predicting human behavior.
possible. http://en.wikipedia.org/wiki/Hard_incompatibilism posits that indeterminism is also incompatible with free will, and thus either way free will is not possible.


This important issue has been widely debated throughout history, including not only whether free will exists but even how to define the concept. Historically, the constraint of dominant concern has been determinism of some variety (such as logical, nomological, or theological), so the most prominent common positions are named for the relation they hold to exist between free will and determinism. Those who define free will as freedom from determinism are called incompatibilists, as they hold determinism to be incompatible with free will. The two main incompatibilist positions are metaphysical libertarianism, the claim that determinism is false and thus free will is at least possible; and hard determinism, the claim that determinism is true and thus free will is not possible. Hard incompatibilism posits that indeterminism is also incompatible with free will, and thus either way free will is not possible.