Both philosophical and everyday reasoning have been haunted by metaphysics for thousands of years, most probably at least since verbal language came into existence. Its roots are perhaps to be found even earlier, because metaphysics, including the mere belief in the supernatural as a different sphere, so to speak, from the physical world, is based upon the ability of recognizing patterns and, most importantly, intentional actors. From the viewpoint of survival, it is more useful to respond to false positives than to false negatives. To flee because you mistake the wind’s noise for a predator will cause you no harm, whereas to stay where you are because you mistake a predator’s noise for the wind will take your genes out of the gene pool.
Unfortunately, while the overly tendency to look for patterns and intentional actors is an advantage with respect to survival, it is, at the same time, an ontological and epistemological disadvantage. From the single, unsystematic beliefs in demons (as a neutral term), later also gods, as intentional actors ‘behind’ natural phenomena, metaphysics has evolved into a systematic absurdity, most prominently represented by Plato’s Realm of Ideas (or Forms) in which the true forms of everything in the physical world exist. Thus, while we, for instance, never encounter a perfect circle but only imperfect circles, in the Realm of Ideas the perfect circle, as the true form, does exist. All imperfect circles in the physical world thus only instantiate the true form as it exists in the Realm of Ideas.1 Plato suggested this theory as a possible solution to the philosophical problem of universals. Yet it is no solution, after all. It is a complication. The remains of this is the in former times plausible but nowadays unjustifiable assumption that everything need a metaphysical backup. This assumption unnecessarily complicates both our ontology and our epistemology. The same holds true for religiously inspired metaphysics.
Notoriously, no one has ever come up with a detailed analysis or description of how, exactly, metaphysical entities work in themselves, let alone upon the physical (natural) world. Metaphysical explanations are pseudo-explanations inasmuch as they do not explain anything but only push the explanation one step back. Metaphysics leave us in the dark about the entities they claim to explain by unwarrentedly assuming further entities ‘behind’ or ‘beyond’ the physical phenomena which remain unexplained themselves, so that, instead of one unexplained entity, we end up with two or more unexplained entities.
Furthermore, if the premise that the sphere of the physical (natural) world need a metaphysical backup is true, nothing will prevent a vicious infinite regress. For either the sphere of the physical (natural) world is ontologically self-sufficient, or every sphere needs a backup. Thus, the metaphysical sphere would need a meta-metaphysical support, the meta-metaphysical sphere in its turn a meta-meta-metaphysical support, and so forth ad infinitum.
From a modern point of view, there simply is no justification for the assumption of metaphysical entities or a metaphysical sphere. Either the metaphysical entities or the metaphysical sphere are investigatable, in which case they would belong to the natural world, or they are, as we are so often, albeit inconsistantly, told unfathomable, so that talk about them is simply empty and therefore idle. Consequently, both philosophical and theological metaphysical speculations are but vain endeavours.
1. For a general description confer the overview entry in Stanford Encyclopedia of Philosophy: http://plato.stanford.edu/entries/plato/#PlaCenDoc. For a more elaborate description and discussion see: http://plato.stanford.edu/entries/plato-metaphysics/. See also the entry on Plato in Internet Encyclopedia of Philosophy: http://www.iep.utm.edu/plato/#SH6b.