In McTaggartian philosophy of time,
- An A-series ordering is an ordering in terms of the following predicates: is past, is present, and is future.
- A B-series ordering is an ordering in terms of the following predicates: comes before and comes after.
- A C-series ordering simply is the very simple concept of any ordering of things.
Only the A-series has direction, but the A-series (according to McTaggart) has no order without the C-series. The conjunction of A-series and C-series produces the B-series. "Beginning" is a B-series concept because it refers to that which comes before all else in time. Yet, B-series depends on A-series and C-series. According to McTaggart, A-series ordering is essential to the reality of time such that, likewise, A-series is essential to the reality of beginnings. Therein, the reality of beginnings depends on the reality of time. I will not take a position either way, but I implore you [impersonal pronoun] to read McTaggart's "The Unreality of Time" and make a judgment on the matter for yourself.
Much more generally, if beginnings exist then, categorically, time exists, and if time begins then something that begins exists, but whether or not anything other than time has a beginning is a separate matter. Additionally, whether or not something that exists is real is another matter entirely (and one that is quite relevant for a realist).
In keeping with Kantian thought, the position expressed herein is that existence/being is not a predicate—“Sein ist offenbar kein reales Prädikat” (Kant 1781). Rather, it merely is copular. It indicates something’s inclusion/exclusion in/from a particular domain of discourse (or universe of objects)—“Es ist bloß die Position eines Dinges oder gewisser Bestimmungen an sich selbst” (Kant 1781). Russell’s (1903) Lotzean distinction between being and existence is rejected on the grounds that it amounts to contradictions (e.g. “nonexistent things must exist as something and every thing is something”) and ill-formed propositions (e.g. “it is”). Moreover, conjugations of "to be" are more versatile than conjugations of "to exist" such that the former can substitute for the latter in virtually every case whereas the latter cannot substitute for the former in many cases.
Thinkers like Parmenides denied the reality of time (and space) such that nothing real begins or ends because beginnings and endings are references to time. Beginnings and endings are illusory; they exist as illusions (i.e. unreal things). Mactaggart argued against the reality of time on the basis of the unreality of referents of time-orderings in terms of past, present, and future (i.e. A-series time-ordering).