An exceedingly simple argument for idealism
1. Something is
2. Nothing is not
3. Something cannot come from nothing
4. Therefore something has primacy
5. Something is only ever known or experienced
6. Anything not known or experienced can only ever be an inference
7. Even an inference is only known or experienced
8. Therefore knowing or experiencing has primacy
Commentary:
1. "Something is." "Something" can mean anything: matter, physical laws, information, a void or vacuum, consciousness, mind. It can be, as Buddhists say, "empty" in the sense of lacking inherent existence, or completely self-existent and "real" as materialists might contend. Regardless of its presumed nature or ontological status, there is indisputably something happening or appearing to arise (and to change, and to ultimately pass). There is simply no reasonable, coherent, or serious way to dispute this basic fact.
2. "Nothing is not." As long as something is present, "nothing" cannot be present, just as complete darkness and light cannot be simultaneously present: light is the absence of darkness, and darkness is the absence of light. The only way "nothing" can ever be present is as a conceptual inference regarding seeming gaps in experience (e.g., deep sleep and general anesthesia) or as an imagined/speculated void prior to the existence of any discrete thing (see next comment).
3. "Something cannot come from nothing." This is the first statement that is likely to prove contentious. But it's crucial to note that a putative "nothing" that includes the very potential for something is, by definition, not truly nothing because potential itself (e.g. action potential or energy potential) is still something. Thus, a quantum fluctuation of the vacuum is not nothing; physical or other foundational laws are not nothing; Platonic ideals or mathematical truths are not nothing; even the notion that "nothing" itself is intrinsically unstable due to the lack any laws or constraints keeping it that way is still not nothing.
4. "Therefore something has primacy." It follows from the preceding premises that "something"—even if considered to be pure potential for manifestation—must be fundamental.
5. "Something is only ever known or experienced." While this might be seen as begging the question, it must be borne in mind that even the mere positing of something outside of experience is still an experience, as is any investigation to confirm or disconfirm something outside of experience. So, for example, it has happened many times that a scientific prediction is made which concerns a phenomenon that's never before been observed, and later that prediction proves true. But both the prediction itself (which is "something") as well as its eventual confirmation (also "something") are, first and foremost, experiences being had.
6. "Anything not known or experienced can only ever be an inference." This seems as if it should be uncontroversial, as long as one doesn't commit the fallacy of assuming that an unusually strong, well-founded inference is some kind of overwhelming evidence that there can be something outside of experience. Because, again, inferring something outside of experience is unfalsifiable, as in principle anything outside of experience could not be proven other than by experiencing it.
7. "Even an inference is only known or experienced." Following from point from 6. above, it is not really possible to step outside of experience except conceptually, as a sheer abstraction (no matter how plausible or compelling or suggestive)—and any conceptual abstraction is still nothing other than an experience.
8. "Therefore, knowing or experiencing has primacy." It follows from the preceding premises that if something has primacy, and something can only even be known or experienced, the fundamental nature of reality must be knowing or experiencing.
One further note:
The most common objection that comes up in discussions around this topic is that it's attempting to derive an ontology from epistemological limitations. As I see it, though, this objection has the same fatal flaw as materialism itself, in that it assumes it's at least possible (if not actually probable) for something to exist irrespective of how or even whether it's known to exist. Elsewhere I've referred to the so-called "hard problem of consciousness" as a flat-earth problem that's vexing only to the degree that it's utterly misconceived in the first place (i.e., it's based on the problematic assumption that matter is real and primary, and consciousness is derivative of it). In this same way, I think that the very distinction between epistemology and ontology is academic and pointless since it seems incoherent to posit the existence of something that even in principle couldn't be known—let alone to grant ontological primacy to it.