Scientific observations are the fuel which power scientific discoveries and scientific theories are the engine. Theories allow scientists to organize and understand earlier observations, then predict and create future observations. Scientific theories all have common characteristics which differentiate them from unscientific ideas like faith and pseudoscience. Scientific theories must be: consistent, parsimonious, correctable, empirically testable/verifiable, useful, and progressive.
1. What Is a Scientific Theory?
Scientists don't use the term "theory" in the same way that it's used in the vernacular. In most contexts, a theory is a vague and fuzzy idea about how things work â€" one with a low probability of being true. This is the origin of complaints that something in science is "only a theory" and so isn't credible. For scientists, a theory is a conceptual structure used to explain existing facts and predict new ones. According to Robert Root-Bernstein in his essay, "On Defining a Scientific Theory: Creationism Considered," to be considered a scientific theory by most scientists and philosophers of science, a theory must meet most, if not all, of certain logical, empirical, sociological and historical criteria.
2. Logical Criteria of Scientific Theories
A scientific theory must be:
- a simple unifying idea that postulates nothing unnecessary (Occam's Razor)
- logically consistent
- logically falsifiable (cases must exist in which the theory can be imagined to be invalid)
- clearly limited by explicit boundary conditions so that it is clear whether or not particular data are or are not relevant to verification or falsification
The logical criteria are cited in discussions about the nature of scientific theories and how science differs from nonscience or pseudoscience. If a theory includes unnecessary ideas or is inconsistent, it can't really explain anything. Without falsifiable, it is impossible to tell if it is true or not, so we correct it via experimentation.
3. Empirical Criteria of Scientific Theories
A scientific theory must:
- be empirically testable or lead to testable predictions or retrodictions (use present information or ideas to infer or explain a past event or state of affairs)
- make verified predictions and/or retrodictions
- have reproducible results
- have criteria for interpreting data as factual, artifactual, anomalous or irrelevant
A scientific theory must help us understand the nature of our data. Some data may be factual (verify the theory's predictions or retrodictions); some may be artifactual (result of secondary or accidental influences); some are anomalous (valid, but at odds with predictions or retrodictions); some are irreproducable and thus invalid; and some are irrelevant.
4. Sociological Criteria of Scientific Theories
A scientific theory must:
- resolve recognized problems, paradoxes, and/or anomalies irresolvable on the basis of earlier theories
- pose new set of scientific problems for scientists to work on
- suggest a paradigm or problem solving model to help resolve new problems
- provide definitions of concepts or operations which help other scientists solve problems
Some critics of science see the above criteria as problems, but they underscore how science is done by a community of researchers and that many scientific problems are discovered by the community. A scientific theory must address a genuine problem and must offer a means of resolving it. If there is no actual problem, how can a theory qualify as scientific?
5. Historical Criteria of Scientific Theories
A scientific theory must:
- meet or surpass all criteria of predecessors or demonstrate that abandoned criteria are artifactual
- explain all data gathered under previous relevant theories in terms either of fact or artifact (no anomalies)
- be consistent with all preexisting, ancillary theories already established as validity
A scientific theory does not just solve a problem, but must do so in a way that is superior to other, competing theories. It must explain more data than the competition; scientists prefer fewer theories which explain more rather than many theories, each of which explains little. This ensures that scientific theories increase in their explanatory power.
6. Legal Criteria of Scientific Theories
Root-Bernstein does not list legal criteria for scientific theories. Ideally there wouldn't be, but Christians have made science a legal issue. In 1981 an Arkansas trial over "equal treatment" for creationism in science classes was overturned and the U.S. Supreme Court ruled such laws were unconstitutional. In his ruling Judge Overton said science has four essential features:
- It is guided by natural laws, and is explanatory by references to natural laws
- Science is testable against the empirical world
- Its conclusions are tentative, not the final word
- It is falsifiable
In the U.S., then, there is a legal basis for answering the question, "what is science?"
7. Summary of Criteria of Scientific Theories
The criteria for scientific theories can be summarized by these principles:
- Consistent (internally & externally)
- Parsimonious (sparing in proposed entities, explanations)
- Useful (describes & explains observed phenomena)
- Empirically Testable & Falsifiable
- Based upon Controlled, Repeated Experiments
- Correctable & Dynamic (changes are made with new data)
- Progressive (achieves all that previous theories have and more)
- Tentative (admits that it might not be correct, does not assert certainty)
These criteria are what we expect for a theory to be considered scientific. Lacking one or two might not mean a theory isn't scientific, but only with good reasons. Lacking most or all is a disqualification.
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