Iron_Captain wrote:
40k certainly has fate as a concept, which is the domain of the god Tzeentch (known as the Architect of Fate). Certainly, Tzeentch himself is above fate, as he is described as the one who weaves the skeins of fate (which may originate from the Well of Eternity mentioned in the Chaos Daemons codex) and interferes in them according to his fulfill his unknowably complex schemes. Since he is said to see all thoughts and dreams and know the future, that also heavily implies a deterministic universe. Tzeentch would not be able to see the future if mortals had a true free will. I'd say that fate is definitely there in
40k, controlled more or less by Tzeentch who is the only one who has the power to command it, albeit an incomplete command, as it is also said there are 'threads of the future' that elude even Tzeentch. Sure, people like Farseers may believe they can see and change the future, but who is to say that their "changing the future" had not been predetermined long ago, and therefore actually was the "default future"?
Tzeentch doesn't know everything as he dunked multiple Changer of Ways into the Well of Eternity until one survived (Kairos Fateweaver) who knows most things (but even then not everything).
In regards to free will, theoretically an omniscient being (which admittedly Tzeentch is not) could know everything that will come to pass and people still have free will. Knowing every detail of everybody and everyone would theoretically allow you to precisely predict every action that would occur. But then Tzeentch is a being of the Warp and as such not bound by the constraints of time.
Since time is somewhat meaningless in the Warp seeing how events would/should unfold would not be beyond the purview of any of the Ruinous Powers. Tzeentch is just the one who most likes to dabble in complex schemes. But he doesn't determine fate (as in 'this will definitely happen' as such. Warhammer
40K generally refutes the concept of a single future being pre-destined (hence the very existence of Farseers).