This chapter begins with enumerating the prerequisites for a critical, rational realism (CRR) derived from a scrutiny of the physics of elementary particles: intelligibility, communicability, correspondence, consistency, coherence, testability. It contends that any physical theory meant to account for the facts and events pertaining to the external world of material objects must invoke those postulates or principles of metaphysical presuppositions—the actually chosen appellation is in this context no more than a question of taste, of personal preference. According to current knowledge, a conservative estimate would show that we have approximately forty kinds of elementary particles. The obvious query which might be prompted by remarks is a hackneyed one: what do we mean by 'real'? At the risk of becoming cumbersome let us nevertheless examine this question as if it were still worthy of rational labor. Common-sense language applies the term to visible, tangible, audible things—to houses, trees, lamps, billiard balls, to stars, peoples: in brief, to material objects.