Metaphysics, or ontology, is the most basic branch of philosophy. It concerns itself with the fundamental nature of existence. Epistemology in contrast, studies the nature and methods of knowledge: What knowledge is, and how best to obtain it.
Metaphysics as a foundation to epistemology consists of two axioms:
I use the term 'stuff' rather than 'things' because it does not suggest that existents or entities are inherent in reality - prior to the application of a given cognitive mechanism, such as the human mind.
All statements about reality that are more specific then these axioms rely on epistemology, and thus have no place in ontology . Examples of such detail include, when and how reality can be meaningfully divided into: waves & particles (or some other categories), physical & mental, or natural & artificial.
Reality can usefully be carved up in an unlimited (though not arbitrary) number of ways. However, all such identifications or classifications assume context and purpose. Context includes issues such as scale, sense modality, perspective, existing knowledge, etc., while purpose may range from conscious & explicit, to implicit & non-conscious.
The simplicity and brevity of these metaphysical statements belie their power. Much philosophical confusion and inefficiency could be eliminated by insisting on these basics.
I believe that Objectivism undermines its clarity and usefulness by inappropriate use of the term 'metaphysical'.
On the one hand there are statements like 'metaphysically significant/ important/ special'. These are contradictions. Evaluations inherently involve knowledge and purpose.
On the other hand we have expressions such as 'metaphysical reality' which falsely imply the possibility of reality that is not metaphysical. This is a confusing redundancy.
Then we have a category of phrases related to volition that suggest remnants of dualism: 'metaphysical versus. man-made (facts)'. Usually what is really meant is the distinction between what is, and what is possible - actual versus potential. 'Man-made' - primarily caused by human action - is a subset of both. It might be epistemologically useful to have a separate concept for things principally caused by, or under the control of, cognition.
Even the, perhaps, legitimate use of 'metaphysically identical' (as opposed to conceptually or informationally) to refer to an identical part of reality, would be better served by describing it as such.
Lastly, I want to address the special ontological status of imagined entities & events. 'Real' is the antonym of 'imagined', and (in philosophy) 'reality' is synonymous with 'existence'. This implies that the imagined does not exist. It is however important to distinguish between the thoughts themselves - which do exist in reality (where else?) – and the things referred to by the thoughts, which do not exist. It gets real complicated when we imagine thoughts or feelings.....
 I regard the identification of consciousness as the fundamental axiom of epistemology. It forms the basis for the crucial distinction between the knower and the known - between (human, animal, or machine) cognition and identified patterns of reality - be they physical or mental, static or dynamic.
 Identical part of reality refers to one and the same section of time-space (or however many dimensions exist).