“Common sense realism” is the important, but mostly forgotten, philosophy of the Scottish thinkers Thomas Reid (1710-96), James Beattie (1735-1803), and Dugald Steward (1753-1828), among others. It stands in striking contrast to the “irrational nonsense” philosophy of Parmenides, Protagoras, Zeno of Elea, Gorgias, Pyrrho, and Sextus Empiricus; as well as Berkeley, Hume, Kant, and Hegel. For the greatness and happiness of the Individual, as well as for the success and harmony of society, it’s crucial that the rational and sensible philosophy of Reid and company triumph.
Common sense realism is essentially a metaphysics and epistemology which is based upon common and universal beliefs which no-one fundamentally or truly doubts, or can reasonably or plausibly deny. This includes such claims as: X is X; X=X; if X, then X; 1+1=2; if A=B and B=C then A=C; existence exists; reality is real; Nature is natural; the universe is fundamentally material; truth and facts exist; the truth is true; facts are factually accurate; things exist; you exist; you’re conscious; you have free will; things change over time; you change over time; living rationally is rational; obeying science is scientific; life is better than death; health is better than disease or injury; pleasure is better than pain; happiness is better than misery; food is better than poison; Michelangelo paints better than an elephant; and The Beatles play better music than a 3-year-old banging on a pot. All such claims are clearly and obviously factually accurate and true to reality, just as all such denials of them lack foundation, soundness, coherence, plausibility, sensibility, logic, reasonableness, objectivity, and tangible evidence.
The philosophy of Common Sense Realism is based upon, and derived from, simple, direct, basic reason, or unambiguous, fundamental logic, or beginning, clear, foundational science. CSR is founded upon self-evidence or self-proving propositions, facts, and truths; upon simple, clear, clean, direct, obvious, undoubtable axioms. To deny or doubt axioms requires immense imagination, delusion, irrationality, and faith. To ask for evidence or proof of axioms is illegitimate, improper, unreasonable, and absurd. The asker isn’t fit for philosophical inquiry or speculation. It isn't necessary -- or even possible -- to stand outside the universe in order to demonstrate something inside it.
If some philosophical claim “flies in the face of all reason” or “denies all common sense” or seems foolish, dumb, irrational, nonsensical, bizarre, or absurd, it must not be accepted as true, or even decently possible, without considerably powerful and persuasive reason, logic, facts, and evidence to back it up. These rarely or never exist.
If some philosophical claim, proposition, or premise asks you to abandon all reason, or suspend all normal judgment, or be intellectually dishonest, evasive, cowardly, and corrupt, then almost certainly this statement is untrue, and even unworthy of consideration. And certainly no claim should be accepted – or even much entertained – based upon mere authority, revelation, or faith – which are all about the same.
Fundamental and foundational truths exist. Initial, known, irrefragable, facts exist. Just as you “can’t prove a negative” so you “can’t prove an axiom”. Nor can you truly doubt one. It’s illegitimate, improper, unphilosophical, unscientific, irrational, and illogical to try. Self-evident truths and axioms are based upon overwhelming and ubiquitous external and internal evidence.