No. That is too different. If something is an act just because it is, it would mean that it would be a potency when it is not. I cannot conceive that.
OK, then this is an issue that we need to discuss, then, because it shows that we have different interpretations of what “act” is.
Since I am trying to defend St. Thomas’ principle, here, we need to understand what St. Thomas meant by act, and for him act is actually
convertible with being: however, with “being” understood as
esse, as existence itself; not “being” understood as
ens (as something that exists).
I will attempt to illustrate here.
Right now, I am at my desk typing. It is rather hot out right now (mid afternoon), and so later on I might go to our swimming pool for a swim. My being in the swimming pool is a realistic possibility for me; I have the means to go into the swimming pool. Nevertheless, right now, I am
not in the swimming pool. (That would be bad for my laptop

.)
Translated into terms of act and potency I would say: right now, I am
actually at my desk (or at my desk “in act”); however, I am only
potentially in the pool (or in the pool “in potency.”)
(On the other hand, although it is not logically contradictory or anything, being in Paris is
not a realistic possibility for me. I can’t afford the plane ticket, and I don’t think my superiors would give my permission to go there in any case, since I don’t have any reason to do so. Hence, I am
not “potentially” in Paris right now.)
That example simply serves to show that, act is actually
identifiable with being (
esse).
To be “in act” is simply “to be a certain way.” Unless I really
am at my desk, I am not
actually at my desk, and vice versa.
I mention this because, for Aquinas, “act” is not limited to operation, even though operation is the most easily recognizable act. This explains why Aquinas calls the root
esse that gives being to all aspects of a thing the
actus essendi.
So, recalling what I said earlier about the logical process used to resolve the different compositions in creatures, the
res significata that is proper to
all act—from operation, to accidental form, to substantial form, to
actus essendi—is precisely that of being (
esse). How the act composes with its proper potency differs, but
all act gives being to the potency it is composed with.
So, regarding your objection:
If something is an act just because it is, it would mean that it would be a potency when it is not. I cannot conceive that.
There is, perhaps, an unfortunate duality in Aristotle and Aquinas’ language as regards potency. We must distinguish
active potency from
passive potency.
I have tried to be careful in our discussions always to call an “active” potency a
power. A “power” is an active capacity to do something, an active capacity for operation (like our intellects and wills).
All of the potencies that I have been discussing here—the antagonists of the various kinds of act—are
passive potencies, potencies that
receive act in some way. These (passive) potencies have included the substance, which is perfected by its accidents; the prime matter, which is perfected by its substantial form; and the essence (considered as a potency), which is perfected by its
actus essendi.
Now, to answer your objection more directly: a thing is in act
precisely because it is (or because it is the way it is). “Potency” (passive potency), as such, is a type of non-being.
So, a thing cannot simply “be a potency,” if you mean by that a “passive”*potency. Take away a thing’s being
relatively, and it will stop being the way it is (e.g., when I move over to the pool, I will stop being
at my desk). Take away a thing’s being
absolutely, and it will stop existing altogether.
However, something can “be a potency” if by that you mean an
active potency, or power. And that is the case of the intellect and will.
In conclusion: the will is indeed “in act” inasmuch as it simply exists, because all act, without exception, is founded on being (
esse). The will’s being is a different
kind of act than its operation, of course, but it is an act all the same.
Does the will “actually” exist? Yes; we say it exists “in act” (
est in actu).
Notice that the will does more than just “exist”: it also tends to the good and has various habits (virtues and vices). Those are also “acts” that are not the will’s operation.