Ontology as I understand it (I am no professional philosopher) is the search for the most fundamental unifying prinicple of reality (being, existence).
For materialism matter is the most unifying concept or principle.
For Idealism, mind is the most unifying concept or principle.
For a process philosophy person like me, it is process (events) which unify reality.
In dealing with ontology, it is always a metaphysical question, and thus lies in the realm of metaphysical assumption or rational speculation but fundamentally is not a scientific question or one solvable by purely objective or empirical means. Ones assumptions about the most unifying or fundamental principle of reality undoubtedly has profound implications in answering other fundamental metaphysical questions (free will, determinism, god, values, ethics, aesthetics, etc.). It is "rough ground".
Heidegger remarks that ontology, the study of being qua being, has become burdened by several thousands of years of philosophical discussion, and thus he suggests that to renew our own thinking we return to the earliest philosophers to whom the subject was fresh. This might well be the "rough ground" of which Wittgenstein writes.
Back to rough ground, except the "ground" is being. We need ontology to find a rough ground? Or are the objects in our everyday life beings? What is it that organizes the flux of sensation into objects in a causal network? I think the TLP is a supreme piece of negative ontology.
Of course there are better and worse ways to consider what beings are, what Being is. From Parmenides to Wittgenstein. Are things anything more than conceptions? What are abstract logical propositions? What sort of being do they have? Abstract being?
Is existence a property? I personally don't need the term ontology, but I'm fond of it.
Anyway, this is a great idea for a thread. Thanks.
Attacks on metaphysics are always metaphysical.