Why do scientific realists think theories should describe reality beyond observable phenomena?

Scientific realists argue that scientific theories should describe reality beyond observable phenomena for several key reasons:

• Explanatory Power: Realists contend that we cannot fully understand or explain phenomena—such as why chemical elements combine in specific ways—without acknowledging the reality of the unobservable entities (like electrons or nuclei) that theories postulate.1
• The "No Miracles" Argument: A central defense of realism is that the immense success of scientific theories would be a "miracle" or a coincidence of cosmic proportions if those theories were not at least approximately true. Realists argue that the most credible explanation for why theories consistently facilitate accurate predictions and technological success is that they accurately describe the underlying structure of the world.23
• Continuity of Observation: Many realists challenge the distinction between observable and unobservable entities. They note that the boundary of what is "observable" shifts with technology (e.g., using microscopes or telescopes). Because there is no sharp, principled division between observing a jet airplane and observing a subatomic particle via a cloud chamber, they argue there is no basis for treating theoretical language about unobservables differently from language about observables.23