“It’s only a theory” is a phrase often used to suggest that the theory in question is weak. This phrase is often used as a response to a theory that one doesn’t agree with or understand. It is imperative to recognize that theory in science is drastically different than the type of theory discussed in everyday conversation. In science, theory represents a body of knowledge that offers an explanation for converging lines of evidence. Science needs theory! Lay person theory (everyday theory) reflects speculation or a guess directed at explaining phenomena.
“Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.” National Center for Science Education
“The formal scientific definition of theory is quite different from the everyday meaning of the word. It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence.” National Academy of Sciences
When juxtaposing lay theory and scientific theory it is evident that they are very different. “It’s only a theory” is a powerful statement in the context of science, as theory represents a high status on the ladder of explanation. It is probably a good idea to abandon the phrase “It’s only a theory” when discussing theories in science. The type of statement is more appropriately directed at lay person theory.
Modern civilization is largely dependent on science and technology. Most people would agree, most of the time. That is, until science repudiates cherished beliefs. Scientific processes are unquestionably the most powerful we have for uncovering reality. Of course, scientific processes demonstrate weaknesses, but they are the best we have for understanding the universe.
Understanding and appreciating the full implications of science, requires, at least, a basic knowledge of the history of science, philosophy of science and matters of scientific literacy. In addition, an understanding of research methodology and statistics will be beneficial in regards to:
Reading scientific journals
Distinguishing science from pseudoscience (in popular science articles)
Protection from quacks
Being a better thinker
Being an independent consumer of research information (you can decide the credibility of the information)
Being a consistent scientific thinker (applying principles of scientific thinking to all contexts)
To learn more about scientific thinking refer to In Evidence We Trust: The Need for ScienceRationality and Statistics